Candies POJ - 3159

版权声明： https://blog.csdn.net/weixin_40959045/article/details/79449426

第一道差分约束

题意：熊孩纸系列…………

    A认为B不会比他多c颗糖及

candies[B] <= candies[A] + C

与d[v] <= d[u] + e.cost 类似

#include <iostream>
#include <vector>
#include <stack>
#include <cstring>
#include <cstdio>
using namespace std;
#define INF 1<<30
#define MAX_V 50000
#define MAX_E 300000
struct edge{
  int v;
  int cost;
  int next;
};
struct edge es[MAX_E];
int head[MAX_V];
int len = 0;
void add(int from,int to,int val)
{
    es[len].v=to;
    es[len].cost =val;
    es[len].next = head[from];
    head[from]=len++;
}
int V;
bool inqueue[MAX_V];
int d[MAX_V];
void spfa(int s){
  for (int i = 0;i<=V;i++)
    d[i] = INF;
  memset(inqueue,0,sizeof inqueue);
  d[s] = 0; inqueue[s] = true;
  stack<int> Q;
  Q.push(s);
  while (!Q.empty()){
    int u = Q.top(); Q.pop();
    inqueue[u] = false;
    for (int i = head[u];i != -1;i = es[i].next){
      int v = es[i].v;
      if (d[v] > d[u] + es[i].cost){
        d[v] = d[u] + es[i].cost;
        if (!inqueue[v]){
          Q.push(v);
          inqueue[v] = true;
        }
      }
    }
  }
}
void init(){
  int M;
  scanf("%d%d",&V,&M);
  memset(head,-1,sizeof head);
  for (int i = 0;i<M;i++){
    int from,to,val;
    scanf("%d%d%d",&from,&to,&val);
    add(from,to,val);
  }
}
int main()
{
  init();
  spfa(1);
  printf("%d\n",d[V]);
  return 0;
}