[2017年杭电多校]Two Paths
Two Paths
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