Implement t sqrt(int x).
Compute and return the square root of x.
题意：求平方根
解析：二分算法，暴力肯定超时
java代码：
public int mySqrt(int x) {
if (x <= 1) {
return x;
}
int begin = 1;
int end = x;
int middle = 0;
while (begin <= end) {
middle = begin + (end - begin) / 2;
if (middle == x / middle) {
return middle;
} else {
if (middle < x / middle) {
begin = middle + 1;
} else {
end = middle - 1;
}
}
}
return end;
}
