Accepted Interview Bit Solution: Shortest common superstring

public class Solution {
    public int solve(ArrayList<String> A) {
        int n = A.size();

        if(n == 1) return A.get(0).length();

        int [][] overlap = new int [n+1][n+1];
        int [][] dp = new int [n+1][(1<<A.size())];

        for(int i=0; i<=n; i++) Arrays.fill(overlap[i], -1);
        for(int i=0; i<=n; i++) Arrays.fill(dp[i], -1);

        int result = Integer.MAX_VALUE;
        for(int i=0; i<A.size(); i++){
            result = Math.min(result, solution(A, i, 0, dp, overlap));
        }
        return result;
    }

    private int solution(ArrayList<String> A, int i, int mask, int [][] dp, int [][] overlap){

        if(dp[i][mask]!= -1) return dp[i][mask];

        int lastmask = (1<<A.size())-1;
        if(mask == lastmask){
            dp[i][mask] = A.get(i).length();
            return dp[i][mask];
        }

        int result = Integer.MAX_VALUE;
        for(int j=0; j<A.size(); j++){
            if((mask&(1<<j)) == 0){
                int value = solution(A, j, (mask|(1<<i)), dp, overlap) +
                            findNonOverLappingLength(A, i, j, overlap);
                result = Math.min(result, value);
            }
        }

        dp[i][mask] = result;
        return dp[i][mask];
    }


    private int findNonOverLappingLength(ArrayList<String> A, int x, int y, int [][] overlap){

        if(overlap[x][y] != -1) return overlap[x][y];

        String a = A.get(x);
        String b = A.get(y);

        if( (a.length() <= b.length()) && b.startsWith(a)) {
            overlap[x][y] = 0;
            return 0;
        }
        else if(a.endsWith(b)) {
            overlap[x][y] = a.length()-b.length();
            return overlap[x][y];
        }

        int len = a.length();
        for(int i=1; i<=b.length(); i++){
            if(i>a.length()) break;
            if(a.endsWith(b.substring(0,i))){
                len = a.length()-i;
            }
        }

        overlap[x][y] = len;
        return len;
    }
}