二分法求平方根的整数部分
int mySqrt(int x) {
int left = 0;
int right = x;
while (left <= right) {
int mid = (left + right) / 2;
if (mid*mid == x) {
return mid;
}
else if (mid*mid < x) {
left = mid + 1;
}
else {
right = mid - 1;
}
}
return right;
}