#include <iostream>
using namespace std;
const int N = 1010;
int n, m;
int v[N], w[N];
int f[N][N];
int main(){
    cin >> n >> m;
    for(int i = 1; i <= n; i ++) cin >> v[i] >> w[i];
    for(int i = 1; i <= n; i ++){
        for(int j = 1; j <= m; j ++){
            f[i][j] = f[i - 1][j];
            if(j >= v[i]) f[i][j] = max(f[i][j], f[i - 1][j - v[i]] + w[i]);
        }
    }
    cout << f[n][m];
    return 0;
}

有点疑问

f[i][j] = f[i - 1][j];

这里不是已经为i-1了吗，为什么后面max的时候还要f[i-1]