976. Largest Perimeter Triangle

题目

Given an array A of positive lengths, return the largest perimeter of a triangle with non-zero area, formed from 3 of these lengths.

If it is impossible to form any triangle of non-zero area, return 0.

Example 1:

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

Example 2:

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

Example 3:

Input: [3,2,3,4]
Output: 10

Example 4:

Input: [3,6,2,3]
Output: 8

Note:

• 3 <= A.length <= 10000
• 1 <= A[i] <= 10^6

题目大意

找到可以组成三角形三条边的长度，要求输出三条边之和最长的，即三角形周长最长。

解题思路

这道题也是排序题，先讲所有的长度进行排序，从大边开始往前找，找到第一个任意两边之和大于第三边(满足能构成三角形的条件)的下标，然后输出这 3 条边之和即可，如果没有找到输出 0 。

代码

package leetcode

func largestPerimeter(A []int) int {
	if len(A) < 3 {
		return 0
	}
	quickSort164(A, 0, len(A)-1)
	for i := len(A) - 1; i >= 2; i-- {
		if (A[i]+A[i-1] > A[i-2]) && (A[i]+A[i-2] > A[i-1]) && (A[i-2]+A[i-1] > A[i]) {
			return A[i] + A[i-1] + A[i-2]
		}
	}
	return 0
}

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