不懂就问

for(int j=0;j<=m;j++)

//100pts
#include <bits/stdc++.h>
using namespace std;
struct node{
	int z,num;
}mon[205];
int n,m,f[205][20005];

int main()
{
	memset(f,0x3f,sizeof(f));
	scanf("%d",&n);
	for(int i=1;i<=n;i++) scanf("%d",&mon[i].z);
	for(int i=1;i<=n;i++) scanf("%d",&mon[i].num);
	scanf("%d",&m);
	for(int i=1;i<=n;i++) mon[i].num=min(mon[i].num,m/mon[i].z);
	for(int i=0;i<=n;i++) f[i][0]=0;
	for(int i=1;i<=n;i++)
	{
		for(int j=0;j<=m;j++)
			for(int k=0;k<=mon[i].num&&k*mon[i].z<=j;k++)
			{
				if(f[i][j]>f[i-1][j-k*mon[i].z]+k) f[i][j]=f[i-1][j-k*mon[i].z]+k;
				//cout<<i<<" "<<j<<" "<<k<<" "<<f[i][j]<<endl;
				//cout<<f[i-1][j]<<" "<<f[i-1][j-k*mon[i].z]+mon[i].num<<endl;
				}
	}
	cout<<f[n][m];
	return 0;
}

//81pts
#include <bits/stdc++.h>
using namespace std;
struct node{
	int z,num;
}mon[205];
int n,m,f[205][20005];

int main()
{
	memset(f,0x3f,sizeof(f));
	scanf("%d",&n);
	for(int i=1;i<=n;i++) scanf("%d",&mon[i].z);
	for(int i=1;i<=n;i++) scanf("%d",&mon[i].num);
	scanf("%d",&m);
	//for(int i=1;i<=n;i++) mon[i].num=min(mon[i].num,m/mon[i].z);
	for(int i=0;i<=n;i++) f[i][0]=0;
	for(int i=1;i<=n;i++)
	{
		for(int j=mon[i].z;j<=m;j++)
			for(int k=0;k<=mon[i].num&&k*mon[i].z<=j;k++)
			{
				if(f[i][j]>f[i-1][j-k*mon[i].z]+k) f[i][j]=f[i-1][j-k*mon[i].z]+k;
				//cout<<i<<" "<<j<<" "<<k<<" "<<f[i][j]<<endl;
				//cout<<f[i-1][j]<<" "<<f[i-1][j-k*mon[i].z]+mon[i].num<<endl;
				}
	}
	cout<<f[n][m];
	return 0;
}