HDU 6181 Two Paths【次短路】【模板题】

Two Paths

Time Limit: 4000/2000 MS (Java/Others)    Memory Limit: 153428/153428 K (Java/Others)
Total Submission(s): 236    Accepted Submission(s): 138

Problem Description

You are given a undirected graph with n nodes (numbered from 1 to n) and m edges. Alice and Bob are now trying to play a game. 
Both of them will take different route from 1 to n (not necessary simple).
Alice always moves first and she is so clever that take one of the shortest path from 1 to n.
Now is the Bob's turn. Help Bob to take possible shortest route from 1 to n.
There's neither multiple edges nor self-loops.
Two paths S and T are considered different if and only if there is an integer i, so that the i-th edge of S is not the same as the i-th edge of T or one of them doesn't exist.

 

Input

The first line of input contains an integer T(1 <= T <= 15), the number of test cases.
The first line of each test case contains 2 integers n, m (2 <= n, m <= 100000), number of nodes and number of edges. Each of the next m lines contains 3 integers a, b, w (1 <= a, b <= n, 1 <= w <= 1000000000), this means that there's an edge between node a and node b and its length is w.
It is guaranteed that there is at least one path from 1 to n.
Sum of n over all test cases is less than 250000 and sum of m over all test cases is less than 350000.

 

Output

For each test case print length of valid shortest path in one line.

 

Sample Input

2 3 3 1 2 1 2 3 4 1 3 3 2 1 1 2 1

 

Sample Output

5 3

Hint

For testcase 1, Alice take path 1 - 3 and its length is 3, and then Bob will take path 1 - 2 - 3 and its length is 5. For testcase 2, Bob will take route 1 - 2 - 1 - 2 and its length is 3

 

Source

2017 Multi-University Training Contest - Team 10

套一个次短路模板即可

#include 
#define INF 1e16+100
#define ms(x,y) memset(x,y,sizeof(x))
using namespace std;

typedef long long ll;
typedef pair P;

const double pi = acos(-1.0);
const int mod = 1e9 + 7;
const int maxn = 1e5 + 5;

struct Edge{
	ll to,cost;
};

ll n,m;
vector a[maxn];
ll dist[maxn],dist2[maxn];

void addedge(ll u,ll v,ll w)
{
	a[u].push_back(Edge{v,w});
	a[v].push_back(Edge{u,w});
}

void solve()
{
	priority_queue, greater
 >que;
	//ms(dist,INF);
	//ms(dist2,INF);
	fill(dist,dist+n,INF);
	fill(dist2,dist2+n,INF);
	dist[0]=0;
	que.push(P(0,0));
	while(que.size())
	{
		P u=que.top();que.pop();
		int v=u.second;
		ll d=u.first;
		if(dist2[v]d2)	//更新最短
			{
				swap(dist[e.to],d2);
				que.push(P(dist[e.to],e.to));
			}
			if(dist2[e.to]>d2&&dist[e.to]

转载于:https://www.cnblogs.com/Archger/p/8451561.html