[LeetCode]Sqrt(x)

Sqrt(x)

Implement int sqrt(int x).

Compute and return the square root of x.

分析

显然用Binary Search解决。

Follow up

Implement double sqrt(double x, int p)
如果结果是res, 必须满足res*res与x直到小数点后p位结果都相同。

同样用Binary Search解决，但要注意精确度，为了符合条件，可以直接将两个结果分别乘以10的p次方，看两者结果整数部分是否相等。

复杂度

time: O(logn), space: O(1)

代码

public class Solution {
    public int mySqrt(int x) {
        int i = 1;
        int j = x;
        
        while (i <= j) {
            int mid = i + (j - i) / 2;
            if (mid == x / mid)
                return mid;
            if (mid < x / mid) {
                i = mid + 1;
            } else {
                j = mid - 1;
            }
        }
        return j;
    }
}

Follow up

public class Solution {
    public double sqrt(double num, int p) {
        double i = 0;
        double j = num;
        double mid = 0;
        while(i <= j) {
            mid = i + (j - i) / 2.0;
            int curVal = (int) (mid * mid * Math.pow(10, p));
            int nextVal = (int) (num * Math.pow(10, p));
            if (curVal == nextVal)
                break;
            if (mid * mid > num) {
                j = mid;
            } else {
                i = mid;
            }
        }
        return mid;
    }
}