使用二分法实现
function mySqrt (num){
let n = Number(num);
if(isNaN(n) || n < 0) return NaN;
if(n == 0 || n == 1) return n;
let up = n,
down = 0,
result = up / 2,
last = result;
do{
if(Math.pow(result,2) > n){
up = result;
}else if(Math.pow(result,2) < n){
down = result;
}else{
return result
}
last = result;
result = (up + down) / 2;
}
while(Math.abs(result - last) >= Number.EPSILON);
return last;
}
