611. Valid Triangle Number

JIAKAOBO

LeetCode

感谢赞助!

• ㊗️
• 大家
• offer
• 多多！

Problem

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

Code

class Solution {
    public int triangleNumber(int[] nums) {
        Arrays.sort(nums);

        int res = 0;
        for (int i = nums.length - 1; i >= 2; i--) {
            int left = 0;
            int right = i - 1;
            while (left < right) {
                if (nums[left] + nums[right] > nums[i]) {
                    res += right - left;
                    right--;
                } else {
                    left++;
                }
            }
        }
        
        return res;
    }
}