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"title": "Maximum Deletions on a String",
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"content": "<p>You are given a string <code>s</code> consisting of only lowercase English letters. In one operation, you can:</p>\n\n<ul>\n\t<li>Delete <strong>the entire string</strong> <code>s</code>, or</li>\n\t<li>Delete the <strong>first</strong> <code>i</code> letters of <code>s</code> if the first <code>i</code> letters of <code>s</code> are <strong>equal</strong> to the following <code>i</code> letters in <code>s</code>, for any <code>i</code> in the range <code>1 <= i <= s.length / 2</code>.</li>\n</ul>\n\n<p>For example, if <code>s = "ababc"</code>, then in one operation, you could delete the first two letters of <code>s</code> to get <code>"abc"</code>, since the first two letters of <code>s</code> and the following two letters of <code>s</code> are both equal to <code>"ab"</code>.</p>\n\n<p>Return <em>the <strong>maximum</strong> number of operations needed to delete all of </em><code>s</code>.</p>\n\n<p> </p>\n<p><strong class=\"example\">Example 1:</strong></p>\n\n<pre>\n<strong>Input:</strong> s = "abcabcdabc"\n<strong>Output:</strong> 2\n<strong>Explanation:</strong>\n- Delete the first 3 letters ("abc") since the next 3 letters are equal. Now, s = "abcdabc".\n- Delete all the letters.\nWe used 2 operations so return 2. It can be proven that 2 is the maximum number of operations needed.\nNote that in the second operation we cannot delete "abc" again because the next occurrence of "abc" does not happen in the next 3 letters.\n</pre>\n\n<p><strong class=\"example\">Example 2:</strong></p>\n\n<pre>\n<strong>Input:</strong> s = "aaabaab"\n<strong>Output:</strong> 4\n<strong>Explanation:</strong>\n- Delete the first letter ("a") since the next letter is equal. Now, s = "aabaab".\n- Delete the first 3 letters ("aab") since the next 3 letters are equal. Now, s = "aab".\n- Delete the first letter ("a") since the next letter is equal. Now, s = "ab".\n- Delete all the letters.\nWe used 4 operations so return 4. It can be proven that 4 is the maximum number of operations needed.\n</pre>\n\n<p><strong class=\"example\">Example 3:</strong></p>\n\n<pre>\n<strong>Input:</strong> s = "aaaaa"\n<strong>Output:</strong> 5\n<strong>Explanation:</strong> In each operation, we can delete the first letter of s.\n</pre>\n\n<p> </p>\n<p><strong>Constraints:</strong></p>\n\n<ul>\n\t<li><code>1 <= s.length <= 4000</code></li>\n\t<li><code>s</code> consists only of lowercase English letters.</li>\n</ul>\n",
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"hints": [
"We can use dynamic programming to find the answer. Create a 0-indexed dp array where dp[i] represents the maximum number of moves needed to remove the first i + 1 letters from s.",
"What should we do if there is an i where it is impossible to remove the first i + 1 letters?",
"Use a sentinel value such as -1 to show that it is impossible.",
"How can we quickly determine if two substrings of s are equal? We can use hashing."
],
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