学步园

#include<cstdio>
#include<cstring>
#include<iostream>
#include<cmath>
#include<string>
#include<vector>
#include<queue>
#include<map>
#include<algorithm>
using namespace std;
inline int Rint() { int x; scanf("%d", &x); return x; }
#define FOR(i, a, b) for(int i=(a); i<=(b); i++)
#define FORD(i,a,b) for(int i=(a);i>=(b);i--)
#define REP(x) for(int i=0; i<(x); i++)
typedef long long int64;
#define INF (1<<30)
const double eps = 1e-8;
#define bug(s) cout<<#s<<"="<<s<<" "

#define MAXN 102
#define MAXM 10002
struct node
{
	int u, v, w;
} edge[MAXM];
int head[MAXN], next[MAXM];
int idx;
int n, m;
void init() {
	idx = 0;
	memset(head, -1, sizeof(head));
}
void addedge(int u, int v, int w) {
	edge[idx].u = u; edge[idx].v = v; edge[idx].w = w;
	next[idx] = head[u]; head[u] = idx++;
}

int dist[MAXN];

// bellman_ford，O(nm)
void bellman_ford(int st) {
	REP(n)
		dist[i] = i==st? 0 : INF;
	FOR(k, 1, n-1) {
		FOR(e, 0, idx-1) {
			int u = edge[e].u, v = edge[e].v;
			dist[v] = min(dist[v], dist[u]+edge[e].w);
		}
	}
}

// dijkstra，O(n^2)
int ins[MAXN];
void dijkstra(int st) {
	memset(ins, 0, sizeof(ins));
	REP(n) dist[i] = i==st? 0 : INF;
	REP(n) {
		int u=-1;
		FOR(j, 0, n-1) if(!ins[j]) {
			if(u==-1) u=j;
			u = dist[u]>dist[j]? j : u;
		}
		ins[u] = 1;
		for(int e=head[u]; e!=-1; e=next[e]) {
			int v = edge[e].v;
			dist[v] = min(dist[v], dist[u]+edge[e].w);
		}
	}
}

// floyd，点对，O(n^3)
int dis[MAXN][MAXN];
void readgraph() {
	FOR(i, 0, n-1)
		FOR(j, 0, n-1) {
			dis[i][j] = INF>>1;
		}
	REP(m) {
		int u = Rint();
		int v = Rint();
		int w = Rint();
		u--, v--;
		dis[u][v] = min(dis[u][v], w);
		dis[v][u] = dis[u][v];
	}
}
void floyd() {
	FOR(k, 0, n-1)
		FOR(i, 0, n-1)
			FOR(j, 0, n-1) {
				dis[i][j] = min(dis[i][j], dis[i][k]+dis[k][j]);
			}
}

// spfa (bellman-ford + queue)，O(km)，k~=2
int que[MAXN], front, tail;
int inq[MAXN];
void spfa(int st) {
	front = tail = 0;
	memset(inq, 0, sizeof(inq));
	REP(n) dist[i] = i==st? 0 : INF;
	que[(tail++)%MAXN] = st;
	inq[st] = 1;
	while(front%MAXN != tail%MAXN) {
		int u = que[(front++)%MAXN];
		inq[u] = 0;
		for(int e=head[u]; e!=-1; e=next[e]) {
			int v = edge[e].v;
			if(dist[v]>dist[u]+edge[e].w) {
				dist[v] = dist[u]+edge[e].w;
				if(!inq[v]) {	// 加了这个，才能保证queue里不超过n个点
					que[(tail++)%MAXN] = v;
					inq[v] = 1;
				}
			}
		}
	}
}

// dijkstra + heap（STL,priority_queue），O(nlogn)
typedef pair<int,int> pii;
#define mp(a,b) make_pair((a),(b))
priority_queue<pii, vector<pii>, greater<pii> > q;
/*
priority_queue 对于基本类型的使用方法相对简单。他的模板声明带有三个参数:
priority_queue<Type, Container, Functional>
其中Type 为数据类型， Container 为保存数据的容器，Functional 为元素比较方式。
Container 必须是用数组实现的容器，比如 vector, deque 但不能用 list.
STL里面默认用的是 vector. 比较方式默认用 operator< , 
所以如果你把后面俩个参数缺省的话，优先队列就是大顶堆，队头元素最大。
*/
void dijkstra_heap(int st) {
	memset(ins, 0, sizeof(ins));
	REP(n) dist[i] = i==st? 0 : INF;
	q.push(mp(dist[st], st));
	while(!q.empty()) {
		pii p = q.top(); q.pop();
		int u = p.second;
		if(ins[u]) continue;
		ins[u] = 1;
		for(int e=head[u]; e!=-1; e=next[e]) {
			int v = edge[e].v;
			if(dist[v]>dist[u]+edge[e].w) {
				dist[v] = dist[u]+edge[e].w;
				q.push(mp(dist[v], v));
			}
		}
	}
}

// HDOJ 2544
int main() {
	while(scanf("%d%d", &n, &m)!=-1 && (n+m)) {
		init();
		REP(m) {
			int u = Rint();
			int v = Rint();
			int w = Rint();
			u--, v--;
			addedge(u, v, w);
			addedge(v, u, w);
		}
		// bellman_ford(0);
		// dijkstra(0);
		// spfa(0);
		dijkstra_heap(0);
		printf("%d\n", dist[n-1]);

		// readgraph();
		// floyd();
		// printf("%d\n", dis[0][n-1]);
	}
}