976. Largest Perimeter Triangle

Easy

Given an integer array nums, return the largest perimeter of a triangle with a non-zero area, formed from three of these lengths. If it is impossible to form any triangle of a non-zero area, return 0.

Example 1:

Input: nums = [2,1,2]
Output:
 5

Example 2:

Input: nums = [1,2,1]
Output:
 0

Constraints:

• 3 <= nums.length <= 104

• 1 <= nums[i] <= 106

解法

三角形成立條件為：任意兩邊長度相加皆大於第三邊

進行排序後，取最大的比較是否小於第二大、第三大的數字，若小於的話即符合構成三角形的條件。

func largestPerimeter(nums []int) int {
	sort.Ints(nums)

	for i := len(nums) - 1; i >= 2; i-- {
		if nums[i] < nums[i-1]+nums[i-2] {
			return nums[i] + nums[i-1] + nums[i-2]
		}
	}

	return 0
}