public int minDistance(String word1, String word2) {
        // write your code here
        int[][] dp = new int[word1.length() + 1][word2.length() + 1];
        for (int i = 0; i < word1.length() + 1; ++i)
            dp[i][0] = i;
        for (int i = 0; i < word2.length() + 1; ++i)
            dp[0][i] = i;
        for (int i = 1; i <= word1.length(); ++i) {
            for (int j = 1; j <= word2.length(); ++j) {
                int diff = word1.charAt(i - 1) == word2.charAt(j - 1) ? 0 : 1;
                dp[i][j] = Math.min(1 + Math.min(dp[i][j - 1], dp[i - 1][j]), diff + dp[i - 1][j - 1]);
            }
        }
        return dp[word1.length()][word2.length()];
    }