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# 69. Sqrt(x)

## 題目原文

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.
```

## **解題思路**

{% hint style="info" %}

{% endhint %}

## 程式解答

```cpp
class Solution 
{
public:
    int mySqrt(int x) 
    {
        int left = 0;
        int mid = 0;
        int right = x;
        
        if (x <= 1)
            return x;
        
        while (left < right)
        {
            mid = left + (right - left) / 2;
            if ((x / mid) < mid)
                right = mid;
            else if ((x / mid) >= mid)
                left = mid + 1;
        }
        return right - 1;
    }
};
```