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Implement strStr().

Returns a pointer to the first occurrence of needle in haystack, or null if needle is not part of haystack.

 Goal: Determine whether needle is substring of haystack or not &
    return the substring(i) i is first occurrence of needle in haystack
    Idea: Use KMP algorithm is an optimal Approach to solve this problem
    but since there is no time complexity requirement in problem.
    Approach:
    we can use brute force approach instead.
    Check match in haystack with needle every time in lengt of needle using
    nested for loop + boolean variable as a checker to skip unmatched
    Time Complexity: O(n*m)
    Space: O(1)

public class Solution {
    public String strStr(String haystack, String needle) {
          if(needle.length()==0) return haystack;
        int hLen=haystack.length();
        int nLen=needle.length();
       if(nLen>hLen){  return null;}
        for(int i=0;i<=hLen-nLen;i++){
            boolean checker=true;
            //check the subString in length of needle
            for(int j=0;j<nLen;j++){
                //skip it if they are unmatched
                if(haystack.charAt(i+j)!=needle.charAt(j)){
                    checker=false;
                    break;
                }
            }
            if(checker){
                return haystack.substring(i);
            }
        }
        return null;
    }
}


本文标签： implementstrStrJava

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