# 1064. Fixed Point

<https://leetcode.com/problems/fixed-point>

## Description

Given an array of distinct integers `arr`, where `arr` is sorted in **ascending order**, return the smallest index `i` that satisfies `arr[i] == i`. If there is no such index, return `-1`.

**Example 1:**

```
**Input:** arr = [-10,-5,0,3,7]
**Output:** 3
**Explanation:** For the given array, arr[0] = -10, arr[1] = -5, arr[2] = 0, arr[3] = 3, thus the output is 3.
```

**Example 2:**

```
**Input:** arr = [0,2,5,8,17]
**Output:** 0
**Explanation:** arr[0] = 0, thus the output is 0.
```

**Example 3:**

```
**Input:** arr = [-10,-5,3,4,7,9]
**Output:** -1
**Explanation:** There is no such i that arr[i] == i, thus the output is -1.
```

**Constraints:**

* `1 <= arr.length < 104`
* `-109 <= arr[i] <= 109`

**Follow up:** The `O(n)` solution is very straightforward. Can we do better?

## ac

```java
```