leetcode/java/367_Valid_Perfect_Square.java at master · cphysics/leetcode

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https://leetcode.com/problems/logger-rate-limiter/

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

Binary search the range from 1 to n inclusive. Use long for mid to avoid overflow with mid * mid.

Return false if left and right are inverted.

Time - O(log n)

Space - O(1)

public class Solution {

public boolean isPerfectSquare(int num) {

long left = 1;

long right = num;

while (left <= right) {

long mid = left + (right - left) / 2;

if (mid * mid == num)

return true;

else if (mid * mid > num) // mid too big, sqrt(num) must be LHS of mid

right = mid - 1;

else

left = mid + 1;

}

return false;

}