# 367.Valid-Perfect-Square

## ้ข็ฎๅฐๅ

https://leetcode.com/problems/valid-perfect-square/

## ้ข็ฎๆ่ฟฐ

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

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

Example 1:
Input: 16
Output: true

Example 2:
Input: 14
Output: false``````

## ไปฃ็ 

``````class Solution {
public boolean isPerfectSquare(int num) {
if (num < 2)    return true;

long left = 2, right = num / 2;
int x, guessSquared;
while (left <= right) {
x = left + (right - left) / 2;
guessSquared = x * x;
if (guessSquared == num) {
return true;
}
if (guessSquared > num) {
right = x - 1;
} else {
left = x  + 1;
}
}

return false;
}
}``````

### Approach #2 Newton's Method

Time `O(logN)` Space `O(1)`

``````class Solution {
public boolean isPerfectSquare(int num) {
if (nums < 2) return true;

long x = num / 2;
while (x * x > num) {
x = (x + num / x) / 2;
}

return (x * x == num);
}
}``````

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