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<p>You are given a string <code>s</code> and a robot that currently holds an empty string <code>t</code>. Apply one of the following operations until <code>s</code> and <code>t</code> <strong>are both empty</strong>:</p>
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<ul>
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<li>Remove the <strong>first</strong> character of a string <code>s</code> and give it to the robot. The robot will append this character to the string <code>t</code>.</li>
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<li>Remove the <strong>last</strong> character of a string <code>t</code> and give it to the robot. The robot will write this character on paper.</li>
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</ul>
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<p>Return <em>the lexicographically smallest string that can be written on the paper.</em></p>
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<p> </p>
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<p><strong class="example">Example 1:</strong></p>
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<pre>
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<strong>Input:</strong> s = "zza"
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<strong>Output:</strong> "azz"
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<strong>Explanation:</strong> Let p denote the written string.
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Initially p="", s="zza", t="".
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Perform first operation three times p="", s="", t="zza".
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Perform second operation three times p="azz", s="", t="".
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</pre>
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<p><strong class="example">Example 2:</strong></p>
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<pre>
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<strong>Input:</strong> s = "bac"
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<strong>Output:</strong> "abc"
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<strong>Explanation:</strong> Let p denote the written string.
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Perform first operation twice p="", s="c", t="ba".
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Perform second operation twice p="ab", s="c", t="".
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Perform first operation p="ab", s="", t="c".
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Perform second operation p="abc", s="", t="".
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</pre>
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<p><strong class="example">Example 3:</strong></p>
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<pre>
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<strong>Input:</strong> s = "bdda"
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<strong>Output:</strong> "addb"
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<strong>Explanation:</strong> Let p denote the written string.
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Initially p="", s="bdda", t="".
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Perform first operation four times p="", s="", t="bdda".
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Perform second operation four times p="addb", s="", t="".
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</pre>
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<p> </p>
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<p><strong>Constraints:</strong></p>
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<ul>
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<li><code>1 <= s.length <= 10<sup>5</sup></code></li>
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<li><code>s</code> consists of only English lowercase letters.</li>
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</ul>
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<p>There are <code>n</code> employees, each with a unique id from <code>0</code> to <code>n - 1</code>.</p>
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<p>You are given a 2D integer array <code>logs</code> where <code>logs[i] = [id<sub>i</sub>, leaveTime<sub>i</sub>]</code> where:</p>
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<ul>
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<li><code>id<sub>i</sub></code> is the id of the employee that worked on the <code>i<sup>th</sup></code> task, and</li>
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<li><code>leaveTime<sub>i</sub></code> is the time at which the employee finished the <code>i<sup>th</sup></code> task. All the values <code>leaveTime<sub>i</sub></code> are <strong>unique</strong>.</li>
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</ul>
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<p>Note that the <code>i<sup>th</sup></code> task starts the moment right after the <code>(i - 1)<sup>th</sup></code> task ends, and the <code>0<sup>th</sup></code> task starts at time <code>0</code>.</p>
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<p>Return <em>the id of the employee that worked the task with the longest time.</em> If there is a tie between two or more employees, return<em> the <strong>smallest</strong> id among them</em>.</p>
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<p> </p>
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<p><strong class="example">Example 1:</strong></p>
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<pre>
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<strong>Input:</strong> n = 10, logs = [[0,3],[2,5],[0,9],[1,15]]
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<strong>Output:</strong> 1
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<strong>Explanation:</strong>
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Task 0 started at 0 and ended at 3 with 3 units of times.
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Task 1 started at 3 and ended at 5 with 2 units of times.
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Task 2 started at 5 and ended at 9 with 4 units of times.
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Task 3 started at 9 and ended at 15 with 6 units of times.
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The task with the longest time is task 3 and the employee with id 1 is the one that worked on it, so we return 1.
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</pre>
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<p><strong class="example">Example 2:</strong></p>
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<pre>
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<strong>Input:</strong> n = 26, logs = [[1,1],[3,7],[2,12],[7,17]]
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<strong>Output:</strong> 3
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<strong>Explanation:</strong>
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Task 0 started at 0 and ended at 1 with 1 unit of times.
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Task 1 started at 1 and ended at 7 with 6 units of times.
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Task 2 started at 7 and ended at 12 with 5 units of times.
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Task 3 started at 12 and ended at 17 with 5 units of times.
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The tasks with the longest time is task 1. The employees that worked on it is 3, so we return 3.
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</pre>
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<p><strong class="example">Example 3:</strong></p>
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<pre>
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<strong>Input:</strong> n = 2, logs = [[0,10],[1,20]]
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<strong>Output:</strong> 0
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<strong>Explanation:</strong>
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Task 0 started at 0 and ended at 10 with 10 units of times.
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Task 1 started at 10 and ended at 20 with 10 units of times.
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The tasks with the longest time are tasks 0 and 1. The employees that worked on them are 0 and 1, so we return the smallest id 0.
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</pre>
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<p> </p>
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<p><strong>Constraints:</strong></p>
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<ul>
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<li><code>2 <= n <= 500</code></li>
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<li><code>1 <= logs.length <= 500</code></li>
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<li><code>logs[i].length == 2</code></li>
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<li><code>0 <= id<sub>i</sub> <= n - 1</code></li>
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<li><code>1 <= leaveTime<sub>i</sub> <= 500</code></li>
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<li><code>id<sub>i</sub> != id<sub>i+1</sub></code></li>
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<li><code>leaveTime<sub>i</sub></code> are sorted in a strictly increasing order.</li>
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</ul>
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<p>You are given an <strong>integer</strong> array <code>pref</code> of size <code>n</code>. Find and return <em>the array </em><code>arr</code><em> of size </em><code>n</code><em> that satisfies</em>:</p>
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<ul>
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<li><code>pref[i] = arr[0] ^ arr[1] ^ ... ^ arr[i]</code>.</li>
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</ul>
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<p>Note that <code>^</code> denotes the <strong>bitwise-xor</strong> operation.</p>
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<p>It can be proven that the answer is <strong>unique</strong>.</p>
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<p> </p>
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<p><strong class="example">Example 1:</strong></p>
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<pre>
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<strong>Input:</strong> pref = [5,2,0,3,1]
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<strong>Output:</strong> [5,7,2,3,2]
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<strong>Explanation:</strong> From the array [5,7,2,3,2] we have the following:
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- pref[0] = 5.
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- pref[1] = 5 ^ 7 = 2.
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- pref[2] = 5 ^ 7 ^ 2 = 0.
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- pref[3] = 5 ^ 7 ^ 2 ^ 3 = 3.
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- pref[4] = 5 ^ 7 ^ 2 ^ 3 ^ 2 = 1.
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</pre>
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<p><strong class="example">Example 2:</strong></p>
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<pre>
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<strong>Input:</strong> pref = [13]
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<strong>Output:</strong> [13]
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<strong>Explanation:</strong> We have pref[0] = arr[0] = 13.
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</pre>
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<p> </p>
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<p><strong>Constraints:</strong></p>
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<ul>
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<li><code>1 <= pref.length <= 10<sup>5</sup></code></li>
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<li><code>0 <= pref[i] <= 10<sup>6</sup></code></li>
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</ul>
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<p>You are given a <strong>0-indexed</strong> <code>m x n</code> integer matrix <code>grid</code> and an integer <code>k</code>. You are currently at position <code>(0, 0)</code> and you want to reach position <code>(m - 1, n - 1)</code> moving only <strong>down</strong> or <strong>right</strong>.</p>
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<p>Return<em> the number of paths where the sum of the elements on the path is divisible by </em><code>k</code>. Since the answer may be very large, return it <strong>modulo</strong> <code>10<sup>9</sup> + 7</code>.</p>
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<p> </p>
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<p><strong class="example">Example 1:</strong></p>
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<img src="https://assets.leetcode.com/uploads/2022/08/13/image-20220813183124-1.png" style="width: 437px; height: 200px;" />
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<pre>
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<strong>Input:</strong> grid = [[5,2,4],[3,0,5],[0,7,2]], k = 3
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<strong>Output:</strong> 2
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<strong>Explanation:</strong> There are two paths where the sum of the elements on the path is divisible by k.
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The first path highlighted in red has a sum of 5 + 2 + 4 + 5 + 2 = 18 which is divisible by 3.
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The second path highlighted in blue has a sum of 5 + 3 + 0 + 5 + 2 = 15 which is divisible by 3.
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</pre>
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<p><strong class="example">Example 2:</strong></p>
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<img src="https://assets.leetcode.com/uploads/2022/08/17/image-20220817112930-3.png" style="height: 85px; width: 132px;" />
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<pre>
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<strong>Input:</strong> grid = [[0,0]], k = 5
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<strong>Output:</strong> 1
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<strong>Explanation:</strong> The path highlighted in red has a sum of 0 + 0 = 0 which is divisible by 5.
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</pre>
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<p><strong class="example">Example 3:</strong></p>
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<img src="https://assets.leetcode.com/uploads/2022/08/12/image-20220812224605-3.png" style="width: 257px; height: 200px;" />
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<pre>
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<strong>Input:</strong> grid = [[7,3,4,9],[2,3,6,2],[2,3,7,0]], k = 1
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<strong>Output:</strong> 10
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<strong>Explanation:</strong> Every integer is divisible by 1 so the sum of the elements on every possible path is divisible by k.
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</pre>
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<p> </p>
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<p><strong>Constraints:</strong></p>
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<ul>
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<li><code>m == grid.length</code></li>
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<li><code>n == grid[i].length</code></li>
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<li><code>1 <= m, n <= 5 * 10<sup>4</sup></code></li>
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<li><code>1 <= m * n <= 5 * 10<sup>4</sup></code></li>
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<li><code>0 <= grid[i][j] <= 100</code></li>
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<li><code>1 <= k <= 50</code></li>
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</ul>
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<p>You are given an integer array <code>coins</code> representing coins of different denominations and an integer <code>amount</code> representing a total amount of money.</p>
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<p>Return <em>the number of combinations that make up that amount</em>. If that amount of money cannot be made up by any combination of the coins, return <code>0</code>.</p>
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<p>You may assume that you have an infinite number of each kind of coin.</p>
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<p>The answer is <strong>guaranteed</strong> to fit into a signed <strong>32-bit</strong> integer.</p>
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<p> </p>
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<p><strong class="example">Example 1:</strong></p>
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<pre>
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<strong>Input:</strong> amount = 5, coins = [1,2,5]
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<strong>Output:</strong> 4
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<strong>Explanation:</strong> there are four ways to make up the amount:
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5=5
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5=2+2+1
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5=2+1+1+1
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5=1+1+1+1+1
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</pre>
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<p><strong class="example">Example 2:</strong></p>
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<pre>
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<strong>Input:</strong> amount = 3, coins = [2]
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<strong>Output:</strong> 0
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<strong>Explanation:</strong> the amount of 3 cannot be made up just with coins of 2.
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</pre>
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<p><strong class="example">Example 3:</strong></p>
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<pre>
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<strong>Input:</strong> amount = 10, coins = [10]
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<strong>Output:</strong> 1
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</pre>
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<p> </p>
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<p><strong>Constraints:</strong></p>
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<ul>
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<li><code>1 <= coins.length <= 300</code></li>
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<li><code>1 <= coins[i] <= 5000</code></li>
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<li>All the values of <code>coins</code> are <strong>unique</strong>.</li>
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<li><code>0 <= amount <= 5000</code></li>
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</ul>
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