69.x的平方根 367.完全有效的平方数

 题目:69. x 的平方根 - 力扣（L69eetCode）

 经典平方根问题，用二分法慢慢逼近找开方值，注意mid*mid要用long long值，不然会溢出

class Solution {
public:int mySqrt(int x) {int left = 0; int right = x;int ans = -1; while( left <= right ){int mid = left + (right - left)/2;//防止溢出if((long long) mid * mid <= x){ans = mid;left = mid + 1;}else right = mid -1;}return ans;//保留小的}
};

此题的推广367. 有效的完全平方数 - 力扣（LeetCode）

只要把想等的情况单拧出来就可以了

class Solution {
public:bool isPerfectSquare(int num) {int left = 0; int right = num;while( left <= right ){int mid = left + (right - left)/2;//防止溢出if((long long) mid * mid == num)return true;if((long long) mid * mid < num)left = mid + 1;else right = mid -1;}return false;}
};