69. Sqrt(x)

Implement int sqrt(int x).

Compute and return the square root of x.

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BST

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public static int helper(int x, int l, int r) {

        if (l < 1 || r > x || l > r)    return Math.min(l, r); // x=2, rst=1, x=8, rst=2;

        int mid = l + (r - l) / 2;

        if (x / mid == mid)         return mid;
        else if (x / mid < mid)        return helper(x, l, mid-1);
        else                        return helper(x, mid+1, r);

    }