题目链接：完全背包问题

初版(时间复杂度拉满)

#include <iostream>
#include <algorithm>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 = 0; j <= m; j ++)for(int k = 0; k * v[i] <= j; k ++)f[i][j] = max(f[i][j], f[i - 1][j - k * v[i]] + k * w[i]);cout << f[n][m] << endl;return 0;
}

改良版

#include <iostream>
#include <algorithm>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 = 0; j <= m; j++){f[i][j] = f[i - 1][j];if(j >= v[i])f[i][j] = max(f[i][j], f[i][j - v[i]] + w[i]);}cout << f[n][m] << endl;return 0;
}

最终版

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