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题目

求一个字符串中，某一个子串它的下标，如果有，则返回这个子串首次出现的下标，如果没有，就返回-1

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"

Input: haystack = "aaaaa", needle = "bba"

代码实现

【解一】

public class demo{		public static int strStr(String s1,String s2){				String s3 = "";		int len = 0;		int index = 0;		int result = 0;		int i = 0;		int j = 0;				if(s2.length()>s1.length()) {			return -2;		}else if(s2=="") {			return -3;		}else {			for(;i
   
    =0){			System.out.println("该字符串出现的第一个位置为:"+(result-s2.length()));		}else if(result==-3){			System.out.println("该字符串出现的第一个位置为:"+0);		}else {			System.out.println("请输入正确的字符串");		}	}}
   

【解二】

public class demo{	public static void main(String[] args) {		String hayStack = "helohello";		String needle = "ello";				int pl = 0;		int index = 0;							for (int i = 0; i < hayStack.length(); i++) {			index = i;			String str = "";						for (int j = i; str.length() < needle.length(); j--) {				if (j >= 0) {					str = hayStack.charAt(j) + str;				}else {					break;				}									}			if (needle.equals(str)) {				pl = 1;				break;			}else {				pl = 0;			}		}		if (needle == "") {			System.out.println("0");		}else if (pl == 1) {			System.out.println(index+1-needle.length());		}else {			System.out.println(-1);		}	}			}

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