Just use the Newton's method

  • 3
    class Solution {
        int sqrt(int x) {
            double res = 1;
            while (abs(res/2+x/(2*res) - res) > 0.1) {
                res = res/2+x/(2*res);
            if ((int)res*(int)res > x) res--;
            return (int)res;

    This is my code.

  • 0

    what is the runtime complexity?

  • 3

    The convergence rate of the Newton's method is at least quadratic. So I think the complexity is likely to be log. However, we can also use the binary search method to obtain this complexity.

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