Two Pointers/Valid Triangle NumberMedium

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Valid Triangle Number

Two Pointers·Medium

Given an integer array nums, return the number of triplets chosen from the array that can make triangles if we take them as the side lengths of a triangle.

Three side lengths a, b, c form a valid triangle iff a + b > c, a + c > b, and b + c > a. After sorting, this reduces to checking only a + b > c for the largest side c.

Examples

Input: nums = [2,2,3,4]

Output: 3

Valid combinations: (2,3,4), (2,3,4), (2,2,3).

Input: nums = [4,2,3,4]

Output: 4

Input: nums = [0,0,0]

Output: 0

Constraints

1 <= nums.length <= 1000
0 <= nums[i] <= 1000

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Tests

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Passed32 ms

First attempt — retry to track metric movement here.

Your approach

Pattern:Two Pointers
Time:O(N)
Space:O(1)

Complete approach — pattern and complexity both named.

Coach

What you got right

You correctly matched the sorted input requirement and implemented a linear-time scan using two pointers.

Where it diverged

No divergence detected. The code correctly aligns with the stated approach.

Next attempt: focus on

Try solving related sliding window problems to build familiarity with two-pointer variants.

Signals

No signals fired — clean run, you stayed in flow.