leetcode 102: Substring with Concatenation of All Words

Substring with Concatenation of All WordsFeb 24 '12

You are given a string, S, and a list of words, L, that are all of the same length. Find all starting indices of substring(s) in S that is a concatenation of each word in L exactly once and without any intervening characters.

For example, given:
S: "barfoothefoobarman"
L: ["foo", "bar"]

You should return the indices: [0,9].
(order does not matter).

public class Solution {
    public ArrayList<Integer> findSubstring(String S, String[] L) {
        // Start typing your Java solution below
        // DO NOT write main() function
        ArrayList<Integer> res = new ArrayList<Integer>();
        if(S==null || L==null || L.length==0) return res;
        
        HashMap<String, Integer> map = new HashMap<String, Integer>();
        
        for(int i=0; i<L.length; i++){
            if(map.containsKey( L[i] ) ){
                map.put(L[i], map.get(L[i])+1);
            } else {
                map.put(L[i], 1);
            }
        }
        
        int sz= S.length();
        int m=L[0].length();
        int n=L.length;
        
        for(int i=0; i<sz-n*m+1;i++) {
            HashMap<String, Integer> temp = new HashMap<String, Integer>(map);
            for(int j=i; j<i+n*m;j+=m) {
                String t = S.substring(j,j+m);
                if( temp.containsKey(t) ){
                    int x=temp.get(t);
                    if(x==1) temp.remove(t);
                    else temp.put(t, x-1);
                } else {
                    break;
                }             
                if(temp.isEmpty()) {
                    res.add(i);
                }
            }
        }
        return res;
    }
}