题目：
Implement int sqrt(int x).
Compute and return the square root of x, where x is guaranteed to be a non-negative integer.
Since the return type is an integer, the decimal digits are truncated and only the integer part of the result is returned.
Example 1:
Input: 4 Output: 2
Example 2:
Input: 8 Output: 2 Explanation: The square root of 8 is 2.82842..., and since the decimal part is truncated, 2 is returned.
代码：
方法一：（普通解法）
class Solution {
public:
int mySqrt(int x) {
long int i = 0;
for(;i*i<=x;i++){}
return i - 1;
}
};方法二：（二分搜索法）
class Solution {
public:
int mySqrt(int x) {
if (x <= 1) return x;
int left = 0, right = x;
while (left < right) {
int mid = left + (right - left) / 2;
if (x / mid >= mid) left = mid + 1;
else right = mid;
}
return right - 1;
}
};想法：
二分搜索法在这道题是最好的，最快的。