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by Sumit Chourasia | Nov 21, 2020 | Category :coding | Tags : algorithm array data-structure leetcode medium

Valid Triangle Number - Array - Medium - LeetCode

Valid Triangle Number - Array - Medium - LeetCode

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

public class Solution {
    public int TriangleNumber(int[] nums) {
        Array.Sort(nums);
        int count = 0;
        for(int i=nums.Length-1;i>=2;i--){
            int l=0;
            int r = i-1;
            while(l<r){
                if(nums[l]+nums[r]>nums[i]){
                    count+= r-l;
                    r--;
                }
                else{
                    l++;
                }                
            }
        }
        
        return count;
    }
}

Time Complexity: O(n^2)

Space Complexity: O(1)