LeetCode 1064. Fixed Point Solution in Java, C++, Python & More | Explanation + Code

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?

Solutions

Solution 1

PythonJavaC++GoTypeScript

class Solution: def fixedPoint(self, arr: List[int]) -> int: left, right = 0, len(arr) - 1 while left < right: mid = (left + right) >> 1 if arr[mid] >= mid: right = mid else: left = mid + 1 return left if arr[left] == left else -1(code-box)

class Solution { public int fixedPoint(int[] arr) { int left = 0, right = arr.length - 1; while (left < right) { int mid = (left + right) >> 1; if (arr[mid] >= mid) { right = mid; } else { left = mid + 1; } } return arr[left] == left ? left : -1; } }(code-box)

class Solution { public: int fixedPoint(vector<int>& arr) { int left = 0, right = arr.size() - 1; while (left < right) { int mid = left + right >> 1; if (arr[mid] >= mid) { right = mid; } else { left = mid + 1; } } return arr[left] == left ? left : -1; } };(code-box)

func fixedPoint(arr []int) int { left, right := 0, len(arr)-1 for left < right { mid := (left + right) >> 1 if arr[mid] >= mid { right = mid } else { left = mid + 1 } } if arr[left] == left { return left } return -1 }(code-box)

function fixedPoint(arr: number[]): number { let left = 0; let right = arr.length - 1; while (left < right) { const mid = (left + right) >> 1; if (arr[mid] >= mid) { right = mid; } else { left = mid + 1; } } return arr[left] === left ? left : -1; }(code-box)