洛谷P1038神经网络

传送门啦

一个拓扑排序的题，感觉题目好难懂。。。

#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
using namespace std;
const int maxn = 105;

inline int read(){char ch = getchar();int f = 1 , x = 0;while(ch > '9' || ch < '0'){if(ch == '-')f = -1;ch = getchar();}while(ch >= '0' && ch <= '9'){x = (x << 1) + (x << 3) + ch - '0';ch = getchar();}return x * f;}

int n,p,c[maxn],u[maxn],x,y,z;
int head[maxn],tot;
int in[maxn],out[maxn];
bool vis[maxn],flag;

struct Edge{
	int from,to,val,next;
}edge[maxn << 1];

void add(int u,int v,int w){
	edge[++tot].from = u;
	edge[tot].to = v;
	edge[tot].val = w;
	edge[tot].next = head[u];
	head[u] = tot;
}

void dfs(int x){
	for(int i=head[x];i;i=edge[i].next){
		int v = edge[i].to;
		c[v] += edge[i].val * c[x];
		in[v]--;
		if(!in[v] && c[v] - u[v] > 0){
			c[v] -= u[v];
			dfs(v);
		}
	}
}

int main(){
	n = read(); p = read();
	for(int i=1;i<=n;i++) {
		c[i] = read(); u[i] = read();
		if(c[i] > 0)  vis[i] = true;
	}
	for(int i=1;i<=p;i++){
		x = read(); y = read(); z = read();
		add(x , y , z);
		in[y]++; out[x]++;
	}
	for(int i=1;i<=n;i++)
		if(vis[i])  dfs(i);
	for(int i=1;i<=n;i++)
		if(out[i] == 0 && c[i] > 0){
			printf("%d %d\n",i,c[i]);
			flag = true;
		}
	if(!flag)  printf("NULL\n");
	return 0;
}