mirror of
https://gitee.com/coder-xiaomo/leetcode-problemset
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184 lines
18 KiB
JSON
184 lines
18 KiB
JSON
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"title": "Expression Add Operators",
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"content": "<p>Given a string <code>num</code> that contains only digits and an integer <code>target</code>, return <em><strong>all possibilities</strong> to insert the binary operators </em><code>'+'</code><em>, </em><code>'-'</code><em>, and/or </em><code>'*'</code><em> between the digits of </em><code>num</code><em> so that the resultant expression evaluates to the </em><code>target</code><em> value</em>.</p>\n\n<p>Note that operands in the returned expressions <strong>should not</strong> contain leading zeros.</p>\n\n<p> </p>\n<p><strong>Example 1:</strong></p>\n\n<pre>\n<strong>Input:</strong> num = "123", target = 6\n<strong>Output:</strong> ["1*2*3","1+2+3"]\n<strong>Explanation:</strong> Both "1*2*3" and "1+2+3" evaluate to 6.\n</pre>\n\n<p><strong>Example 2:</strong></p>\n\n<pre>\n<strong>Input:</strong> num = "232", target = 8\n<strong>Output:</strong> ["2*3+2","2+3*2"]\n<strong>Explanation:</strong> Both "2*3+2" and "2+3*2" evaluate to 8.\n</pre>\n\n<p><strong>Example 3:</strong></p>\n\n<pre>\n<strong>Input:</strong> num = "3456237490", target = 9191\n<strong>Output:</strong> []\n<strong>Explanation:</strong> There are no expressions that can be created from "3456237490" to evaluate to 9191.\n</pre>\n\n<p> </p>\n<p><strong>Constraints:</strong></p>\n\n<ul>\n\t<li><code>1 <= num.length <= 10</code></li>\n\t<li><code>num</code> consists of only digits.</li>\n\t<li><code>-2<sup>31</sup> <= target <= 2<sup>31</sup> - 1</code></li>\n</ul>\n",
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"exampleTestcases": "\"123\"\n6\n\"232\"\n8\n\"3456237490\"\n9191",
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"categoryTitle": "Algorithms",
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"code": "class Solution {\npublic:\n vector<string> addOperators(string num, int target) {\n \n }\n};",
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"code": "class Solution {\n\n /**\n * @param String $num\n * @param Integer $target\n * @return String[]\n */\n function addOperators($num, $target) {\n \n }\n}",
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"code": "(define/contract (add-operators num target)\n (-> string? exact-integer? (listof string?))\n\n )",
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"langSlug": "erlang",
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"code": "-spec add_operators(Num :: unicode:unicode_binary(), Target :: integer()) -> [unicode:unicode_binary()].\nadd_operators(Num, Target) ->\n .",
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"code": "defmodule Solution do\n @spec add_operators(num :: String.t, target :: integer) :: [String.t]\n def add_operators(num, target) do\n\n end\nend",
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"hints": [
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"Note that a number can contain multiple digits.",
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"Since the question asks us to find <b>all</b> of the valid expressions, we need a way to iterate over all of them. (<b>Hint:</b> Recursion!)",
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"We can keep track of the expression string and evaluate it at the very end. But that would take a lot of time. Can we keep track of the expression's value as well so as to avoid the evaluation at the very end of recursion?",
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"Think carefully about the multiply operator. It has a higher precedence than the addition and subtraction operators. \r\n\r\n<br> 1 + 2 = 3 <br>\r\n1 + 2 - 4 --> 3 - 4 --> -1 <br>\r\n1 + 2 - 4 * 12 --> -1 * 12 --> -12 (WRONG!) <br>\r\n1 + 2 - 4 * 12 --> -1 - (-4) + (-4 * 12) --> 3 + (-48) --> -45 (CORRECT!)",
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"We simply need to keep track of the last operand in our expression and reverse it's effect on the expression's value while considering the multiply operator."
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"sampleTestCase": "\"123\"\n6",
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