611. Valid Triangle Number

Given an array consists of non-negative integers, your task is to count 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: [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

 Note:

1. The length of the given array won't exceed 1000.
2. The integers in the given array are in the range of [0, 1000]. 

找出满足组成三角形的三条边的个数

 思路：组成三角形条件是两条较短的边的和大于第三条边

    public int triangleNumber(int[] nums) {
        Arrays.sort(nums);
        int count = 0;
        for (int i = nums.length - 1; i >= 2; i--) {
            int left = 0, right = i - 1;
            while (left < right) {
                if (nums[left] + nums[right] > nums[i]) { //最短的两条边之和大于最长的边nums[i]
                    count += right - left; //left后面的数字，都可以结合right构成三角形
                    right--;
                } else {
                    left++;
                }
            }
        }
        return count;
    }