最长公共子序列

#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <string>
using namespace std;
#define N 1005
int dp[N+1][N+1];
int b[N+1][N+1];
char str1[N],str2[N];
void lcs(int len1,int len2)
{
    for(int i=0;i<len1;i++){
        for(int j=0;j<len2;j++){
            if(str1[i]==str2[j]){
                dp[i+1][j+1]=dp[i][j]+1;
                b[i+1][j+1]=1;
            }
            else if(dp[i][j+1]>dp[i+1][j]){
                dp[i+1][j+1]=dp[i][j+1];
                b[i+1][j+1]=2;
            }else{
                dp[i+1][j+1]=dp[i+1][j];
                b[i+1][j+1]=3;
            }
        }
    }
    cout<<dp[len1][len2]<<endl;
}
void printLcs(int i,int j)
{
    if(i==0||j==0) return;
    else if(b[i][j]==1){
        printLcs(i-1,j-1);
        cout<<str1[i-1];
    }else if(b[i][j]==2) printLcs(i-1,j);
    else printLcs(i,j-1);
}
int main()
{
    while(cin>>str1>>str2){
        memset(dp,0,sizeof(dp));
        memset(b,0,sizeof(b));
        int len1=strlen(str1);
        int len2=strlen(str2);
        lcs(len1,len2);//求解序列长度
        printLcs(len1,len2);//打印序列
    }
    return 0;
}