Day8 : 30 Day LeetCode May challenges

problem_statement8.txt

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

Valid_perfect_square.cpp

class Solution {
public:
    bool isPerfectSquare(int num) {
        /*int n = sqrt(num);
        for(int i=1; i<=n; i++){
            if(i*i == num)
                return true;
        }
        return false;
        */
        /*
        int i = 1;
        while (num > 0) {
            num -= i;
            i += 2;
        }
        return num == 0;
        */
        long low = 1, high = num;
        while (low <= high) {
            long mid = (low + high)>>1;//(low+high)/2
            if (mid * mid == num) {
                return true;
            } else if (mid * mid < num) {
                low = (int) mid + 1;
            } else {
                high = (int) mid - 1;
            }
        }
        return false;
    }
};
/*
     int i = 1;
     while (num > 0) {
         num -= i;
         i += 2;
     }
     return num == 0;
The time complexity is O(sqrt(n)), a more efficient one using binary search whose time complexity is O(log(n)):

       
        int low = 1, high = num;
        while (low <= high) {
            long mid = (low + high) >>> 1;
            if (mid * mid == num) {
                return true;
            } else if (mid * mid < num) {
                low = (int) mid + 1;
            } else {
                high = (int) mid - 1;
            }
        }
        return false;
*/