611. Valid Triangle Number

Description

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.

Constraints

• 1 <= nums.length <= 1000

• 0 <= nums[i] <= 1000

Approach

Links

• Binarysearch

• GeeksforGeeks

• Leetcode

• ProgramCreek

• YouTube

Examples

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

Solutions

Solution 1

/**
 * Time complexity : 
 * Space complexity : 
 */

class Solution {
    public int triangleNumber(int[] nums) {
        if(nums == null || nums.length < 3) {
            return 0;
        }
        Arrays.sort(nums);
        int count = 0;
        for(int i = nums.length-1; i >= 2; i--) {
            int l = 0, r = i-1;
            while(l < r) {
                if(nums[l]+nums[r] > nums[i]) {
                    count += r-l;
                    r--;
                } else {
                    l++;
                }
            }
        }
        return count;
    }
}

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