0069-sqrtx.cpp

/*
69. Sqrt(x)

Submitted: February 23, 2025

Runtime: 0 ms (beats 100.00%
Memory: 8.58 MB (beats 51.10%)
*/

// fast inverse square root
doubleQ_rsqrt( double number )
{
long i;
double x2, y;
constdouble threehalfs = 1.5;

 x2 = number * 0.5;
 y = number;
 i = * ( long * ) &y;
 i = 0x5fe6eb50c7b537a9 - ( i >> 1 );
 y = * ( double * ) &i;
 y = y * ( threehalfs - ( x2 * y * y ) ); // 1st iteration
 y = y * ( threehalfs - ( x2 * y * y ) ); // 2nd iteration, this can be removed
 y = y * ( threehalfs - ( x2 * y * y ) ); // added in 3rd iteration so we can pass leetcode testcases
return y;
}

classSolution {
public:
intmySqrt(int x) {
return1.0 / Q_rsqrt(x);
 }
};