POJ1201 Intervals查分约束系统（最短路）

#include <cstdio>
#include <cstring>
#include <algorithm>
#include <queue>
#include <stack>
#include <vector>
using namespace std;
const int INF = 0x3f3f3f3f;
const int N = 5e4 + 10;
struct Edge {
    int v, cost;
    Edge() {}
    Edge(int v, int cost) : v(v), cost(cost) {}
};
vector<Edge> E[N];
void add(int u, int v, int w) {
    E[u].push_back(Edge(v, w));
}
bool vis[N];
int d[N];
void SPFA(int st, int n) {
    memset(vis, false, sizeof vis);
    for(int i = 1; i <= n; ++i) d[i] = -INF;
    d[st] = 0;
    vis[st] = true;
    queue<int> que;
    while(!que.empty()) que.pop();
    que.push(st);
    while(!que.empty()) {
        int u = que.front();
        que.pop();
        vis[u] = false;
        int sx = E[u].size();
        for(int i = 0; i < sx; ++i) {
            int v = E[u][i].v;
            int w = E[u][i].cost;
            if(d[v] < d[u] + w) {
                d[v] = d[u] + w;
                if(!vis[v]) {
                    vis[v] = true;
                    que.push(v);
                }
            }
        }
    }
}
int main() {
    int n;
    while(~scanf("%d", &n)) {
        int a, b, c, m = 0, st = INF;
        for(int i = 0; i < n; ++i) {
            scanf("%d%d%d", &a, &b, &c);
            a+=2; b+=2;
            add(a - 1, b, c);
            m = max(m, b);
            st = min(st, a - 1);
        }
        for(int i = 2; i <= m; ++i) {
            add(i, i - 1, -1);
            add(i - 1, i, 0);
        }
        SPFA(st, m);
        printf("%d\n", d[m]);
    }
    return 0;
}