Sqrt(x) 求平方根@LeetCode

二分法

package Level4;

/**
 * Sqrt(x)
 * 
 * Implement int sqrt(int x).
 * 
 * Compute and return the square root of x.
 * 
 */
public class S69 {

	public static void main(String[] args) {
		System.out.println(sqrt(2));
	}

	public static int sqrt(int x) {
		double diff = 0.01;		// 误差
		int low = 0;
		int high = x;
		
		while(low <= high){
			// 注意越界！所以用double来存
			double mid = low + (high-low)/2;
			if(Math.abs(mid*mid-x) <= diff){
				return (int)mid;
			}else if(x > mid*mid+diff){
				low = (int)mid+1;
			}else if(x < mid*mid-diff){
				high = (int)mid-1;
			}
		}
		
		// 当找不到时候，这是low,high指针已经交叉，取较小的，即high
		return high;
	}

}

public class Solution {
    public int sqrt(int x) {
        int left = 0, right = x;
        while(left <= right) {
            double mid = left + (right-left)/2;
            double mul = mid * mid;
            if(mul == x){
                return (int)mid;
            } else if(mul < x) {
                left = (int)mid+1;
            } else {
                right = (int)mid-1;
            }
        }
        return right;
    }
}