LeetCode in Kotlin

611. Valid Triangle Number

Medium

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

Example 1:

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

Output: 3

Explanation: Valid combinations are:

2,3,4 (using the first 2)

2,3,4 (using the second 2)

2,2,3

Example 2:

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

Output: 4

Constraints:

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

Solution

class Solution {
    fun triangleNumber(nums: IntArray): Int {
        val n: Int
        var max = 0
        val count = IntArray(1001)
        for (i in nums) {
            count[i]++
            max = Math.max(max, i)
        }
        count[0] = 0
        var idx = 0
        for (i in 1..max) {
            var j = 0
            while (j < count[i]) {
                nums[idx] = i
                ++j
                ++idx
            }
            count[i] += count[i - 1]
        }
        n = idx
        var r = 0
        for (i in 0 until n - 2) {
            for (j in i + 1 until n - 1) {
                if (nums[i] + nums[j] > max) {
                    r += (n - j) * (n - j - 1) / 2
                    break
                }
                r += count[nums[i] + nums[j] - 1] - j - 1
            }
        }
        return r
    }
}

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