力扣69x的平方根

Posted 2021-12-03 夏天吃辣椒

1、换函数exp()(0ms,100%;6.2MB,5%)

  int mySqrt(int x) {
         if(x==0)
         return x;
        int num=exp(0.5*log(x));
        if(long (num+1)*(num+1)<=x)
        return num+1;
        else
        return num;
     }

2、二分查找(4ms,59%;5.8MB,64%)

 int mySqrt(int x) {
         if(x<=1)
         return x;
         long left=1,right=x;
         long mid=(left+right)/2;
         while(left<=right){
             //因为很多数的算数平方根是夹在两个数中间的
             if(((mid*mid)<=x)&&((mid+1)*(mid+1)>x))
             return mid;
             //mid偏小，整体往右移动
             else if((mid*mid)<x){
                 left=mid+1;
                 mid=(left+right)/2;
             }
             //mid偏大，整体往右移动
             else {
                 right=mid-1;
                 mid=(left+right)/2;
             }
             
         }
         return 0;
     }

3、牛顿迭代（4ms,59%;5.8MB,60%）:没看懂

 int mySqrt(int x) {
        if (x == 0) {
             return 0;
         }
 
         double C = x, x0 = x;
         while (true) {
             double xi = 0.5 * (x0 + C / x0);
             if (fabs(x0 - xi) < 1e-7) {
                 break;
             }
             x0 = xi;
         }
         return int(x0);
     }