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?

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