Very easy understand.

```
public int minDistance(String word1, String word2) {
int m = word1.length(), n = word2.length();
int[] dp = new int[n + 1];
for (int i = 0; i <= n; i++) dp[i] = i;
for (int i = 1; i <= m; i++) {
int prev = i;
for (int j = 1; j <= n; j++) {
int cur;
if (word1.charAt(i - 1) == word2.charAt(j - 1))
cur = dp[j - 1];
else {
int insert = prev;
int delete = dp[j];
int replace = dp[j - 1];
cur = Math.min(Math.min(insert, delete), replace) + 1;
}
dp[j - 1] = prev;
prev = cur;
}
dp[n] = prev;
}
return dp[n];
}
```