1.4 KiB
1.4 KiB
Leetcode Largest-Perimeter-Triangle
2022-07-26 08:39
Algorithms:
#algorithm #greedy #math
Difficulty:
#coding_problems #difficulty_easy
Additional tags:
#leetcode
Revisions:
N/A
Related topics:
Links:
Problem
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.
Examples
Example 1:
Input: nums = [2,1,2] Output: 5
Example 2:
Input: nums = [1,2,1] Output: 0
Constraints
3 <= nums.length <= 1041 <= nums[i] <= 106
Thoughts
[!summary] This is a #math problem.
After sorting, the answer must be consecutive 3 elements.
Why?
assume l, m , r.
if nums[l] + nums[m] < nums[r], because after sorting, the order is ascending, anything before l and m will not suffice.
Solution
class Solution {
public:
int largestPerimeter(vector<int> &nums) {
sort(nums.begin(), nums.end());
int r = nums.size() - 1;
// change l first until its boundary
for (int i = r; i > 1; i--) {
if (nums[i] < nums[i - 1] + nums[i - 2]) {
return nums[i] + nums[i - 1] + nums[i - 2];
}
}
return 0;
}
};