ACM学习历程—Hihocoder 1139 二分·二分答案（bfs）

#include <iostream>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <cmath>
#include <queue>
#include <map>
#include <set>
#include <string>
#include <vector>
#define LL long long

using namespace std;

const int maxN = 100005;
//链式前向星
struct Edge
{
    int to, next;
    int val;
}edge[maxN*2];

int head[maxN], cnt;

void addEdge(int u, int v, int val)
{
    edge[cnt].to = v;
    edge[cnt].next = head[u];
    edge[cnt].val = val;
    head[u] = cnt;
    cnt++;
}

void initEdge()
{
    memset(head, -1, sizeof(head));
    cnt = 0;
}

int n, m, k, to;
LL dis[maxN];

void input()
{
    initEdge();
    memset(dis, -1, sizeof(dis));
    int u, v, t;
    for (int i = 0; i <= m; ++i)
    {
        scanf("%d%d%d", &u, &v, &t);
        addEdge(u, v, t);
        addEdge(v, u, t);
    }
}

inline LL myMax(LL x, LL y)
{
    return x > y ? x : y;
}

struct Item
{
    int index;
    LL val;
    int step;
};

void work()
{
    int u, v, t, step;
    LL val, len;
    Item p, tmp;
    queue<Item> q;
    dis[1]= 0;
    p.index = 1;
    p.step = 0;
    p.val = 0;
    q.push(p);
    while (!q.empty())
    {
        p = q.front();
        q.pop();
        u = p.index;
        step = p.step;
        val = p.val;
        for (int i = head[u]; i != -1; i = edge[i].next)
        {
            v = edge[i].to;
            len = edge[i].val;
            if (dis[v] == -1 || myMax(val, len) < dis[v])
            {
                dis[v] = myMax(val, len);
                p.index = v;
                p.step = step+1;
                p.val = dis[v];
                if (p.step < k)
                    q.push(p);
            }
        }
    }
    cout << dis[to] << endl;
}

int main()
{
    //freopen("test.in", "r", stdin);
    //freopen("test.out", "w", stdout);
    while (scanf("%d%d%d%d", &n, &m, &k, &to) != EOF)
    {
        input();
        work();
    }
    return 0;
}