leetcode_30 Implement strStr()

本文主要是介绍leetcode_30 Implement strStr()，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！

题目：

Return the index of the first occurrence of needle in haystack, or -1 if needle is not part of haystack.

Example 1:

Input: haystack = "hello", needle = "ll"
Output: 2

Example 2:

Input: haystack = "aaaaa", needle = "bba"
Output: -1

Clarification:

What should we return when needle is an empty string? This is a great question to ask during an interview.

For the purpose of this problem, we will return 0 when needle is an empty string. This is consistent to C's strstr() and Java's indexOf().

采用KMP算法：详见文章strstr的实现--KMP

class Solution {
public:vector<int> getnext(string needle){int n = needle.length();vector<int> lps(n,0);for(int i = 1,len = 0 ; i < n ;){if(needle[i] == needle[len])lps[i++] = ++len;else if(len){len = lps[len - 1];}else{lps[i++] = 0;}}return lps;}int strStr(string haystack, string needle) {int n = needle.length();if(n == 0){return 0;}int h = haystack.length();if(h == 0){return -1;}vector<int> next = getnext(needle);int i, j;for(i = 0,j = 0; i < h ;){if(haystack[i] == needle[j]){i++;j++;}if(j == n)return i - j;if(i < h && haystack[i] != needle[j]){if(j > 0){j = next[j -1];}else{i++;}}}return -1;}
};

这篇关于leetcode_30 Implement strStr()的文章就介绍到这儿，希望我们推荐的文章对编程师们有所帮助！

---