```
public int minDistance(String word1, String word2) {
int n1 = word1.length(), n2 = word2.length(), i, j;
int[][] dp = new int[n1+1][n2+1];
if (n1 == 0 || n2 == 0) {
return n1 + n2;
}
dp[0][0] = 0;
dp[0][1] = 0; dp[1][0] = 0;
for (i=1;i<=n1;i++) {
for (j=1;j<=n2;j++) {
if (word1.charAt(i-1) == word2.charAt(j-1)) {
dp[i][j] = dp[i-1][j-1] + 1;
} else {
dp[i][j] = Math.max(dp[i-1][j], dp[i][j-1]);
}
}
}
return n1 + n2 - 2*dp[n1][n2];
}
}
```