LeetCode算法入門- Implement strStr() -day22

題目描述

Implement strStr().

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().

題目分析：
通過兩個for循環來實現

Java實現：

class Solution {public int strStr(String haystack, String needle) {if(needle.length() == 0){return 0;}for(int i = 0 ; ; i++){for(int j = 0; ; j++){//如果長度相同，說明完全匹配了if(j == needle.length()){return i;}//下面代碼其實就是for循環省去的約束部分if(i + j == haystack.length()){return -1;}//用來判斷對應的字符是不是相同if(haystack.charAt(i + j) != needle.charAt(j)){break;}}}} }

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