leetcode_69

x的平方根
二分法，注意在相等的时候还是需要计算一次

var mySqrt = function(x) {
    let left = 0;
    let right = x;
    let middle=0;
    let result = 0;
    while(left<=right) {
        middle = Math.floor((left+right)/2)
        if(middle*middle<=x) {
            left = middle+1
            result = middle
        } else {
            right=middle-1
        }
    }
    return result
}