public class Solution {

     /**

      * @param word1 & word2: Two string.

      * @return: The minimum number of steps.

      */

     public int minDistance(String word1, String word2) {

         // write your code here

         int[][] dp = new int[word1.length()+1][word2.length()+1];

         for(int i=1;i<=word1.length();i++)

             dp[i][0] = i;

         for(int i=1;i<=word2.length();i++)

             dp[0][i] = i;

         for(int i=0;i<word1.length();i++){

             for(int j=0;j<word2.length();j++){

                 if(word1.charAt(i) == word2.charAt(j)){

                     dp[i+1][j+1] = Math.min(dp[i][j],Math.min(dp[i][j+1],dp[i+1][j])+1);

                 }else{

                     dp[i+1][j+1] = Math.min(dp[i][j+1]+1,Math.min(dp[i][j],dp[i+1][j])+1);

                 }

             }

         }

         return dp[word1.length()][word2.length()];

     }

 }