```
public int minDistance(String word1, String word2) {
int len1 = word1.length();
int len2 = word2.length();
char[] str1 = word1.toCharArray();
char[] str2 = word2.toCharArray();
int[][] dp = new int[len1 + 1][len2 + 1];
// first row
for (int i = 1; i <= len2; i++) {
dp[0][i] = i;
}
// first column
for (int i = 1; i <= len1; i++) {
dp[i][0] = i;
}
for (int i = 1; i <= len1; i++) {
for (int j = 1; j <= len2; j++) {
if (str1[i - 1] == str2[j - 1]) {
dp[i][j] = dp[i - 1][j - 1];
} else {
dp[i][j] = 1 + Math.min(dp[i - 1][j - 1],
Math.min(dp[i - 1][j], dp[i][j - 1]));
}
}
}
return dp[len1][len2];
}
```