mirror of
https://gitee.com/coder-xiaomo/leetcode-problemset
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181 lines
18 KiB
JSON
181 lines
18 KiB
JSON
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"question": {
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"questionId": "2477",
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"questionFrontendId": "2400",
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"boundTopicId": null,
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"title": "Number of Ways to Reach a Position After Exactly k Steps",
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"titleSlug": "number-of-ways-to-reach-a-position-after-exactly-k-steps",
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"content": "<p>You are given two <strong>positive</strong> integers <code>startPos</code> and <code>endPos</code>. Initially, you are standing at position <code>startPos</code> on an <strong>infinite</strong> number line. With one step, you can move either one position to the left, or one position to the right.</p>\n\n<p>Given a positive integer <code>k</code>, return <em>the number of <strong>different</strong> ways to reach the position </em><code>endPos</code><em> starting from </em><code>startPos</code><em>, such that you perform <strong>exactly</strong> </em><code>k</code><em> steps</em>. Since the answer may be very large, return it <strong>modulo</strong> <code>10<sup>9</sup> + 7</code>.</p>\n\n<p>Two ways are considered different if the order of the steps made is not exactly the same.</p>\n\n<p><strong>Note</strong> that the number line includes negative integers.</p>\n\n<p> </p>\n<p><strong class=\"example\">Example 1:</strong></p>\n\n<pre>\n<strong>Input:</strong> startPos = 1, endPos = 2, k = 3\n<strong>Output:</strong> 3\n<strong>Explanation:</strong> We can reach position 2 from 1 in exactly 3 steps in three ways:\n- 1 -> 2 -> 3 -> 2.\n- 1 -> 2 -> 1 -> 2.\n- 1 -> 0 -> 1 -> 2.\nIt can be proven that no other way is possible, so we return 3.</pre>\n\n<p><strong class=\"example\">Example 2:</strong></p>\n\n<pre>\n<strong>Input:</strong> startPos = 2, endPos = 5, k = 10\n<strong>Output:</strong> 0\n<strong>Explanation:</strong> It is impossible to reach position 5 from position 2 in exactly 10 steps.\n</pre>\n\n<p> </p>\n<p><strong>Constraints:</strong></p>\n\n<ul>\n\t<li><code>1 <= startPos, endPos, k <= 1000</code></li>\n</ul>\n",
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"difficulty": "Medium",
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"exampleTestcases": "1\n2\n3\n2\n5\n10",
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"categoryTitle": "Algorithms",
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"code": "class Solution(object):\n def numberOfWays(self, startPos, endPos, k):\n \"\"\"\n :type startPos: int\n :type endPos: int\n :type k: int\n :rtype: int\n \"\"\"\n ",
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"code": "/**\n * @param {number} startPos\n * @param {number} endPos\n * @param {number} k\n * @return {number}\n */\nvar numberOfWays = function(startPos, endPos, k) {\n \n};",
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"code": "class Solution {\n\n /**\n * @param Integer $startPos\n * @param Integer $endPos\n * @param Integer $k\n * @return Integer\n */\n function numberOfWays($startPos, $endPos, $k) {\n \n }\n}",
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"lang": "Ruby",
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"code": "# @param {Integer} start_pos\n# @param {Integer} end_pos\n# @param {Integer} k\n# @return {Integer}\ndef number_of_ways(start_pos, end_pos, k)\n \nend",
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"lang": "Scala",
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"code": "object Solution {\n def numberOfWays(startPos: Int, endPos: Int, k: Int): Int = {\n \n }\n}",
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"code": "impl Solution {\n pub fn number_of_ways(start_pos: i32, end_pos: i32, k: i32) -> i32 {\n \n }\n}",
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"code": "(define/contract (number-of-ways startPos endPos k)\n (-> exact-integer? exact-integer? exact-integer? exact-integer?)\n )",
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"lang": "Erlang",
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"code": "-spec number_of_ways(StartPos :: integer(), EndPos :: integer(), K :: integer()) -> integer().\nnumber_of_ways(StartPos, EndPos, K) ->\n .",
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"lang": "Elixir",
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"langSlug": "elixir",
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"code": "defmodule Solution do\n @spec number_of_ways(start_pos :: integer, end_pos :: integer, k :: integer) :: integer\n def number_of_ways(start_pos, end_pos, k) do\n \n end\nend",
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"hints": [
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"How many steps to the left and to the right do you need to make exactly?",
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"Does the order of the steps matter?",
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"Use combinatorics to find the number of ways to order the steps."
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],
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"solution": null,
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"sampleTestCase": "1\n2\n3",
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