时间复杂度：O(nm)
空间复杂度：O(nm)

class Solution {
public:
    int minDistance(string word1, string word2) {
        int maxlen[555][555];
        int n=word1.length(),m=word2.length();
        for(int i=0;i<=m;i++)
            maxlen[0][i]=0;
        for(int i=0;i<=n;i++)
            maxlen[i][0]=0;
        for(int i=1;i<=n;i++){
            for(int j=1;j<=m;j++){
                if(word1[i-1]==word2[j-1]){
                    maxlen[i][j]=maxlen[i-1][j-1]+1;
                }else{
                    maxlen[i][j]=max(maxlen[i-1][j],maxlen[i][j-1]);
                }
            }
        }
        return n+m-maxlen[n][m]-maxlen[n][m];
    }
};