最长公共子序列 LCS + 路径还原

#include<iostream>
#include<algorithm>
#include<vector>
using namespace std;

vector<vector<int> > dp(1000,vector<int>(1000,0)),mark(1000,vector<int>(1000,0));
string a,b,ans;
void dfs(int i,int j){
	if(i == 0 || j == 0) return;
	if(mark[i][j] == 1){
		dfs(i-1,j-1);
		ans += a[i-1];
	}
	else if(mark[i][j] == 2){
		dfs(i-1,j);
	}
	else{
		dfs(i,j-1);
	}
}
int main()
{
	cin>>a>>b;
	int n = a.length();
	int m = b.length();
	for(int i = 1;i <= n;i ++){
		for(int j = 1;j <= m;j ++){
			if(a[i-1] == b[j - 1]){
				dp[i][j] = dp[i-1][j-1] + 1;
				mark[i][j] = 1;      //来自左上 
			}
			else if(dp[i-1][j] > dp[i][j-1]){
				dp[i][j] = dp[i-1][j];
				mark[i][j] = 2;      //来自上方 
			}
			else{
				dp[i][j] = dp[i][j-1];
				mark[i][j] = 3;		 //来自左方 
			}
		}
	}
	dfs(n,m);
	cout<<dp[n][m]<<endl<<ans<<endl;
	return 0;
}#include<iostream>
#include<algorithm>