leetcode 69. Sqrt(x)

Implement int sqrt(int x).

Compute and return the square root of x.

int mySqrt(int x){if (x == 0)return 0;long long int xx = x;long long int up = xx;long long int down = 0;while (true){if (up*up > xx)up = (up+down)/2;else{int t = down; down = up;up = 2 * up - t;if (up-down==1&&up*up>=xx||up==down)return up*up == x ? up : down;}}}

accepted

类似二分查找，夹逼思想（不要想歪了）