A profile page shows a "mutuals" badge when two users follow each other. You get the follow list follows, where [a, b] means user a follows user b.
Write countMutuals(follows) that returns how many unordered pairs of users follow each other. The pair {a, b} counts once, no matter the order of the two follows.
No follow appears twice and nobody follows themselves.
Input: follows = [[0,1],[1,0],[1,2],[2,3],[3,2]] Output: 2
Users 0 and 1 follow each other, and so do 2 and 3. The follow from 1 to 2 is one way.
Input: follows = [[0,1],[1,2]] Output: 0
No follow goes back the other way.
0 <= follows.length <= 1000000 <= a, b <= 10^9 and a !== bRun tries your code on the examples. Submit runs every test, including hidden edge cases, and solves the problem when they all pass.
Ctrl + Enter runs, Ctrl + Shift + Enter submits (⌘ on a Mac).
I'm here to help with #406 Count Mutual Follows. I give hints, never the solution, so you get to solve it yourself. Ask for a hint, select code to ask about it, or press Ask Tuto why on a failing test.
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