Triangle Triplets - Amazon Top Interview Questions
Problem Statement :
Given a list of non-negative integers nums, return the total number of 3 numbers i < j < k, such that nums[i] + nums[j] > nums[k]. Constraints n ≤ 1,000 where n is the length of nums Example 1 Input nums = [7, 8, 8, 9, 100] Output 4 Explanation We can make these triangles: 7, 8, 8 7, 8, 9 7, 8, 9 (using the other 8) 8, 8, 9
Solution :
Solution in C++ :
int solve(vector<int>& nums) {
sort(nums.begin(), nums.end());
int res = 0;
int n = nums.size();
// triangle inequality: a+b > c
// Fix a c, then count how many (a,b) such that nums[a] + nums[b] > nums[c]
for (int c = n - 1; c >= 0; c--) {
int a = 0;
int b = c - 1;
while (a < b) {
if (nums[a] + nums[b] > nums[c]) {
res += (b - a);
b--;
} else {
a++;
}
}
}
return res;
}
Solution in Python :
class Solution:
def solve(self, nums):
count = 0
nums.sort()
n = len(nums)
for i in range(n - 1, 1, -1):
l, r = 0, i - 1
while l < r:
if nums[l] + nums[r] <= nums[i]:
l += 1
else:
count += r - l
r -= 1
return count
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