LeetCode 1064. Fixed Point

Description

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

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?

Explanation

Just check if the element’s value equals to its index.

Python Solution

class Solution:
    def fixedPoint(self, arr: List[int]) -> int:
        
        for i, num in enumerate(arr):
            if num == i:
                return i
        
        
        return -1
  • Time Complexity: O(N).
  • Space Complexity: O(1).

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