public int getLongestSubString(String s1,String s2){
		if(s1==null||s2==null)return 0;
		int res=0;
		int m=s1.length(),n=s2.length();
		int [][] dp=new int[n][m];
		for (int i = 0; i < n; i++) {
			for (int j = 0; j < m; j++) {
				if(s1.charAt(j)==s2.charAt(i)){
					if(i>0&&j>0)dp[i][j]=dp[i-1][j-1]+1;
					else if (i == 0 || j == 0)dp[i][j] = 1;
				}
				res=Math.max(dp[i][j], res);
			}
			
		}
		return res;
	}