hdu1384查分约束（最短路径）-优快云博客

本文介绍了一种使用 SPFA (Shortest Path Faster Algorithm) 计算最短路径的方法，通过 C++ 实现了从指定起点到最大节点的距离计算，并详细展示了节点结构、边的定义、初始化过程及 SPFA 主算法流程。

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#include <iostream>
#include <cstdio>
#include <cstring>
#include <queue>

using namespace std;

const int MAX = 0x7FFFFFFF;
const int M = 500005;
int head[M];
struct node {

    int to;
    int value;
    int next;
}edge[M];

int n;
int dist[M];
int vist[M];
int cnt;
int maxn, minn;

void init() {

       cnt = 0;
        maxn = -MAX;
        minn = MAX;
    memset(head, -1, sizeof(head));
  //  memset(dist, MAX, sizeof(dist));
    memset(vist, 0, sizeof(vist));

}

void add(int v, int u, int d) {

    edge[cnt].to = u;
    edge[cnt].value = d;
    edge[cnt].next = head[v];
    head[v] = cnt++;
}

void SPFA(int u) {

    for(int i = 0; i <= maxn; i++) {

        dist[i] = -500000;
    }
    queue<int>que;
    while(!que.empty()) que.pop();
    dist[u] = 0;
    vist[u] = 1;
    que.push(u);

    while(!que.empty()) {

        u = que.front();
        que.pop();
        vist[u] = 0;
        for(int k = head[u]; k != -1; k = edge[k].next) {

            int v = edge[k].to;
            int d = edge[k].value;
            if(dist[v] < dist[u] + d) {
             // printf("%d  %d   %d  %d\n", v, u, dist[v], dist[u]);
                dist[v] = dist[u] + d;
                if(vist[v] == 0)
                {
                    vist[v] = 1;
                   que.push(v);
                }

            }

        }
    }
    printf("%d\n", dist[maxn]);
}

int main()
{
    int x, y, d;

    while(scanf("%d", &n) != EOF) {

        init();

        for(int i = 1; i <= n; i++) {

            scanf("%d%d%d", &x, &y, &d);
            minn = min(minn, x);
            maxn = max(y + 1, maxn);
            add(x, y+1, d);
        }

        for(int i = minn; i <= maxn; i++)
        {
            add(i, i+1, 0);
            add(i+1, i, -1);
        }

        SPFA(minn);
    }


    return 0;
}