leetcode 71: 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(L.length<1 || S.length() < L.length*L[0].length() ) return res;
            
        Map<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 i=0;
        int Slen = S.length();
        int Llen = L.length;
        int sz = L[0].length();
        
        while( Slen-i >= Llen*sz){
            
            Map<String, Integer> temp = new HashMap<String,Integer>(map);
            for(int j=0; j<Llen; j++) {
                String sub = S.substring(i+j*sz, i+(j+1)*sz);
                
                if( temp.containsKey(sub) ) {
                    int x = temp.get(sub);
                    if( x>1) 
                        temp.put(sub, temp.get(sub)-1);
                    else if( x==1) 
                        temp.remove( sub);
                }else 
                    break;
            }
            if(temp.isEmpty() ) res.add(i);         
            ++i;
        }
        return res;
    }
}