Counting on a directed graph
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Read problems statements in Mandarin Chinese and Russian.
Given an directed graph with N nodes (numbered from 1 to N) and M edges, calculate the number of unordered pairs (X, Y) such there exist two paths, one from node 1 to node X, and another one from node 1 to node Y, such that they don't share any node except node 1.
There is only one test case in one test file.
The first line of each test case contains two space separated integers N, M. Each of the next M lines contains two space separated integers u, v denoting a directed edge of graph G, from node u to node v. There are no multi-edges and self loops in the graph.
Print a single integer corresponding to the number of unordered pairs as asked in the problem..
Constraints and Subtasks
- 1 ≤ N ≤ 105
- 0 ≤ M ≤ 5 * 105
Subtask 1: (30 points)
- The graph is a Directed Acyclic Graph (DAG) i.e. there is no cycle in the graph.
Subtask 2: (20 points)
- N * M ≤ 50000000
Subtask 3 (50 points)
- No additional constraints
Input: 6 6 1 2 1 3 1 4 2 5 2 6 3 6 Output: 14
There are 14 pairs of vertices as follows:
|Tags||dominator, may15, medium-hard, ztxz16|
|Time Limit:||2 sec|
|Source Limit:||50000 Bytes|
|Languages:||C, CPP14, JAVA, PYTH, PYTH 3.5, PYPY, CS2, PAS fpc, PAS gpc, RUBY, PHP, GO, NODEJS, HASK, SCALA, D, PERL, FORT, WSPC, ADA, CAML, ICK, BF, ASM, CLPS, PRLG, ICON, SCM qobi, PIKE, ST, NICE, LUA, BASH, NEM, LISP sbcl, LISP clisp, SCM guile, JS, ERL, TCL, PERL6, TEXT, SCM chicken, CLOJ, FS|
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