[LeetCode] 367. Valid Perfect Square

轉自LeetCode

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
Returns: True

Example 2:

Input: 14
Returns: False

<Solution>

因為題目有要求不能用 sqrt 來算，這時候就只能用牛頓法來算

code 如下

C++

	class Solution {
	public:
	bool isPerfectSquare(int num) {
	long x = num;
	while(x * x > num) {
	x = (x + num / x) >> 1;
	}
	return x * x == num;
	}
	};

view raw validPerfectSquare.cpp hosted with ❤ by GitHub

用二分法也可以

kotlin

	class Solution {
	fun isPerfectSquare(num: Int): Boolean {
	val longNum = num.toLong()
	var left = 0L
	var right = longNum
	while(left <= right) {
	var mid = left + (right - left) / 2L
	var t = mid * mid
	when {
	t == longNum -> return true
	t < longNum -> left = mid + 1
	else -> right = mid - 1
	}
	}
	return false
	}
	}

view raw valid_perfect_square.kt hosted with ❤ by GitHub