28_Implement strStr

Posted 2020-10-09

/*
 Implement strStr().

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

*/

解决思路：
　　遍历haystack与needle，时间复杂度O（n^2）
　

class Solution {
public:
    int strStr(string haystack, string needle) {
        if(haystack.size()==0 && needle.size()==0) return 0;
        for(int i;i<haystack.size();i++){
            bool label =true;
            for(int j=0;j<needle.size();j++)
                if(haystack[i+j] != needle[j]) {
                    label = false;
                    break;}
            if(label)
                return i; 
        }
        return -1;
    }
};

discussion：

　　题目类似字符串匹配，可参考KMP算法　https://en.wikipedia.org/wiki/Knuth%E2%80%93Morris%E2%80%93Pratt_algorithm