LCS问题

#include <iostream>
#include <algorithm>
#include <cmath>
#include <vector>
#include <string>
#include <cstring>
#pragma warning(disable:4996)
using namespace std;

char a[1005];
char b[1005];
int dp[1005][1005];
int pre[1005][1005];

void dfs(int m,int n)
{
    if(m==0||n==0)
        return;
    if(pre[m][n]==1)
    {
        dfs(m-1,n-1);
        cout<<a[m];
    }
    else if(pre[m][n]==2)
    {
        dfs(m-1,n);
    }
    else
    {
        dfs(m,n-1);
    }
}


int main()
{
    int i,j,len1,len2;
    memset(dp,0,sizeof(dp));
    memset(pre,0,sizeof(pre));

    cin>>a+1>>b+1;

    len1=strlen(a+1);
    len2=strlen(b+1);
    
    for(i=1;i<=len1;i++)
    {
        for(j=1;j<=len2;j++)
        {
            if(a[i]==b[j])
            {
                dp[i][j]=dp[i-1][j-1]+1;
                pre[i][j]=1;
            }
            else
            {
                if(dp[i-1][j]>dp[i][j-1])
                {
                    dp[i][j]=dp[i-1][j];
                    pre[i][j]=2;
                }
                else
                {
                    dp[i][j]=dp[i][j-1];
                    pre[i][j]=3;
                }
            }
        }
    }
    dfs(len1,len2);
    cout<<endl;
    return 0;
}