hiho1093_spfa

#include<stdio.h>
#include<cmath>
#include<iostream>
#include<string.h>
#include<algorithm>
#include<queue>
#include<stack>
#include<map>
#include<deque>
#include<string>
#include<unordered_map>
#include<unordered_set>
using namespace std;

#define max(a, b) (a) > (b)? (a) : (b)
#define min(a, b) (a) < (b)? (a) : (b)
unordered_map<int, unordered_map<int, int>>  gMap;
int gMinDist[100005];
bool gInQueue[100005];
int Spfa(int s, int t) {
	queue<int> Q;
	Q.push(s);
	memset(gMinDist, -1, sizeof(gMinDist));
	memset(gInQueue, false, sizeof(gInQueue));
	gMinDist[s] = 0;
	gInQueue[s] = true;
	//题目中不存在负权边，因此不需要检查有负权回路。检查存在负权回路，则需要通过
	//判断否个点是否被更新超过 N 次，N为点的总数
	while (!Q.empty()) {
		int u = Q.front();
		Q.pop();
		gInQueue[u] = false;
		for (auto x : gMap[u]) {
			int v = x.first;
			if (gMinDist[v] == -1 || gMinDist[v] > gMinDist[u] + x.second) {
				gMinDist[v] = gMinDist[u] + x.second;
				if (!gInQueue[v]) { //如果不存在队列中，则加入队列。剪枝优化
					Q.push(v);
				}
			}
		}
	}
	return gMinDist[t];
}
int main() {
	int n, m, s, t;
	int u, v, d;
	scanf("%d %d %d %d", &n, &m, &s, &t);
	for (int i = 0; i < m; i++) {
		scanf("%d %d %d", &u, &v, &d); //用 unordered_map 存储图的结构，可以方便的去除重边
		if (gMap.find(u) == gMap.end() || (gMap[u].find(v) == gMap[u].end() || gMap[u][v] > d)) {
			gMap[u][v] = d;
			gMap[v][u] = d;
		}
	}
	int min_dist = Spfa(s, t);
	printf("%d\n", min_dist);
	return 0;
}