Fixed point

Array Binary Search

63.8% acceptance

Mar 31, 2026

442

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.

Solution

Rust

Time O(n log n)

Space O(1)

LeetCode

solution.rs

impl Solution {
  pub fn fixed_point(arr: Vec<i32>) -> i32 {
    let mut lo = 0usize;
    let mut hi = arr.len();
    while lo < hi {
      let mid = lo + (hi - lo) / 2;
      if arr[mid] - mid as i32 >= 0 {
        hi = mid;
      } else {
        lo = mid + 1;
      }
    }
    if lo < arr.len() && arr[lo] == lo as i32 { lo as i32 } else { -1 }
  }
}