版权声明:本文为博主原创文章,转载请附上源地址。 https://blog.csdn.net/Ema1997/article/details/79522064
反思:本题图是密集图,所以用queue的时候的log的复杂度就不能忽略了,而且点数不是很多,考虑到这个,就需要用一个数组来模拟操作,来降低复杂度,把log的复杂度变为线性的,其他的没什么了。
#include <iostream>
#include <queue>
#include <cstdio>
#include <map>
#include <cstring>
#include <stack>
#include <string>
#include <vector>
#include <cmath>
using namespace std;
const int INF = 1 << 30;
const int maxn = 30010;
const int maxm = 150010;
struct Edge
{
int v, w;
int next;
Edge(){}
Edge(int vv, int ww, int nn) : v(vv), w(ww), next(nn) {}
};
int n, m;
int head[maxn];
Edge e[maxm];
int dis[maxn];
int q[maxn];
int vis[maxn];
int cnt;
int top;
void Init()
{
top = 0;
cnt = 0;
memset (head, -1, sizeof(head));
for (int i = 1; i<= n; i++) {
dis[i] = INF;
}
}
void add(int u, int v, int w)
{
e[cnt] = Edge(v, w, head[u]);
head[u] = cnt++;
}
void SPFA(int v)
{
memset (vis, 0, sizeof(vis));
q[top++] = v;
dis[v] = 0;
vis[v] = 1;
while (top != 0) {
int t = q[--top];
vis[t] = 0;
for (int i = head[t]; i != -1; i = e[i].next) {
Edge tmp = e[i];
int md = tmp.w + dis[t];
if (md < dis[tmp.v]) {
dis[tmp.v] = md;
if (!vis[tmp.v]) {
vis[tmp.v] = 1;
q[top++] = tmp.v;
}
}
}
}
}
int main()
{
#ifndef ONLINE_JUDGE
freopen("in.txt", "r", stdin);
//freopen("out.txt", "w", stdout);
#endif // ONLINE_JUDGE
scanf ("%d%d", &n, &m);
Init ();
for (int i = 0; i < m; i++) {
int a, b, c;
scanf ("%d%d%d", &a, &b, &c);
add(a, b, c);
}
SPFA (1);
printf ("%d", dis[n]);
return 0;
}