Valid Perfect Square - Math - Easy - LeetCode

1 min read 98 words

sumitc911 October 2020Updated: 1 October 2020 1 min read

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1The function checks if a positive integer is a perfect square without using built-in functions like sqrt.
2It uses a while loop to incrementally sum odd integers until the sum equals or exceeds the input number.
3The solution has a time complexity of O(n) and a space complexity of O(1).

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"The function checks if a positive integer is a perfect square without using built-in functions like sqrt."

— Valid Perfect Square - Math - Easy - LeetCode

Given a positive integer num, write a function that returns True if num is a perfect square else False.

Follow up: Do not use any built-in library function such as sqrt.

Example 1:

Input: num = 16 Output: true Example 2:

Input: num = 14 Output: false

Constraints:

1 <= num <= 2^31 - 1

public class Solution {
 public bool IsPerfectSquare(int num) {
 int i = 1;
 int sum = 0;
 while (sum < num) {
 sum += i;
 if(sum<0){
 return false;
 }
 i += 2;
 }
 return sum==num;
 }
}

Time Complexity: O(n)

Space Complexity: O(1)

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