hiho_1139_二分+bfs搜索

#include<stdio.h>
#include<string.h>
#include<iostream>
#include<string>
#include<set>
#include<map>
#include<vector>
#include<queue>
#include<stack>
#include<unordered_map>
#include<unordered_set>
#include<algorithm>
using namespace std;
struct Edge{
	int to;
	int dist;
	int next;
};
//边的个数，开始的时候数组开的长度为 100005， hihocoder上提示 TLE，实际应该为 RE！！！
//数组开到 200005，就AC了
Edge gEdges[200005];
int gHead[10005];
bool gVisited[10005];
int gEdgeIndex;
void Init(){
	gEdgeIndex = 0;
	memset(gEdges, -1, sizeof(gEdges));
	memset(gHead, -1, sizeof(gHead));
	memset(gVisited, false, sizeof(gVisited));
}
void InsertEdge(int u, int v, int d){
	int e = gEdgeIndex++;
	gEdges[e].to = v;
	gEdges[e].dist = d;
	gEdges[e].next = gHead[u];
	gHead[u] = e;
}
struct Node{
	int id;
	int step;
	Node(int i = 0, int s = 0) :id(i), step(s){};
};
//BFS 搜索，寻找从点1到达点boss的路径，要求路径上的所有边的长度都小于等于max_d，且路径长度最大为k
//判断能否找到满足要求的路径
bool Arrive2Boss(int boss, int max_d, int k){
	queue<Node> Q;
	Node node(1, 1);
	Q.push(node);
	memset(gVisited, false, sizeof(gVisited));
	while (!Q.empty()){
		node = Q.front();
		Q.pop();
		if (node.id == boss)
			return true;
		if (gVisited[node.id])
			continue;
		gVisited[node.id] = true;
		for (int e = gHead[node.id]; e != -1; e = gEdges[e].next){
			int v = gEdges[e].to;
			if (!gVisited[v] && gEdges[e].dist <= max_d && node.step <= k){
				Q.push(Node(v, node.step + 1));
			}
		}
	}
	return false;
}
int edges_len[100005];
int main(){
	int N, M, K, T, u, v, d;
	Init();
	scanf("%d %d %d %d", &N, &M, &K, &T);
	for (int i = 0; i < M; i++){
		scanf("%d %d %d", &u, &v, &d);
		InsertEdge(u, v, d);
		InsertEdge(v, u, d);
		edges_len[i] = d;
	}
	//对路径进行排序
	sort(edges_len, edges_len + M);
	int beg = 0, end = M;
	//二分查找
	while (beg < end){
		int mid = (beg + end) / 2;
		int max_d = edges_len[mid];
		if (Arrive2Boss(T, max_d, K)){
			end = mid;
		}
		else
			beg = mid + 1;
	}
	int result = edges_len[beg];
	printf("%d\n", result);
	return 0;
}