POJ-3159 Candies

题目大意：

有n个小孩，m个约束条件，每个约束条件为A B C表示A认为B不应该比自己多超过C个糖。问你1号小孩和n号小孩最多相差多少个糖

解题思路：

差分约束

代码：

#include <cstdio>
#include <cstring>
using namespace std;

const int INF = 0x3f3f3f3f;
const int maxn = 30000 + 5;
const int maxm = 150000 + 5;

typedef struct node{
int to, w;
int next;
}Edge;

int tol;
Edge edge[maxm];
int s[maxm], head[maxm], dis[maxn], vis[maxn];

void add(int a, int b, int c){
edge[tol].to = b;
edge[tol].w = c;
edge[tol].next = head[a];
head[a] = tol++;
}
int spfa(int n){
int p, v, top = 0;
for(int i = 0; i <= n; ++i){
dis[i] = INF;
vis[i] = 0;
}
dis[1] = 0; vis[1] = 1; s[top++] = 1;

while(top){
p = s[--top]; vis[p] = 0;
for(int i = head[p]; ~i; i = edge[i].next){
v = edge[i].to;
if(dis[v] > dis[p] + edge[i].w){
dis[v] = dis[p] + edge[i].w;

if(!vis[v]){
vis[v] = 1;
s[top++] = v;
}
}
}
}
return dis
;
}
int main(){
tol = 0;
int a, b, c, n, m;

scanf("%d%d", &n, &m);
memset(head, -1, sizeof(head));

for(int i = 0; i < m; ++i){
scanf("%d%d%d", &a, &b, &c);
add(a, b, c);
}
printf("%d\n", spfa(n));
return 0;
}