976.Largest Perimeter Triangle

Tags: Easy Array

Links: https://leetcode.com/problems/largest-perimeter-triangle/

---

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:

1. 3 <= A.length <= 10000
2. 1 <= A[i] <= 10^6

---

class Solution {
public:
    int largestPerimeter(vector<int>& A) {
        sort(A.begin(), A.end());
        int res = 0;
        int n = A.size();
        for (int i = n - 1; i >= 2; --i) {
            if (A[i] < A[i - 1] + A[i - 2]) {
                res = A[i] + A[i-1] + A[i - 2];
                break;
            }
        }

        return res;
    }
};

考虑和leetcode611对比分析，不同场景下三角形问题的变形。