Guess the majority in a hidden array

Array Math Interactive

68.8% acceptance

Mar 31, 2026

147

122

// This is the ArrayReader's API interface. // You should not implement it, or speculate about its implementation struct ArrayReader; impl ArrayReader { // Compares 4 different elements in the array // return 4 if the values of the 4 elements are the same (0 or 1). // return 2 if three elements have a value equal to 0 and one element has value equal to 1 or vice versa. // return 0 : if two element have a value equal to 0 and two elements have a value equal to 1. pub fn query(a: i32, b: i32, c: i32, d: i32) -> i32 {} // Returns the length of the array pub fn length() -> i32 {} };

Solution

Rust

Time O(n)

Space O(1)

LeetCode

solution.rs

impl Solution {
  pub fn get_majority(reader: &ArrayReader) -> i32 {
    let n = reader.length();
    let base = reader.query(0, 1, 2, 3);

    let mut same_count = 1;
    let mut diff_count = 0;
    let mut diff_index = -1;

    let same_as_zero_for_four = reader.query(1, 2, 3, 4) == base;
    if same_as_zero_for_four {
      same_count += 1;
    } else {
      diff_count += 1;
      diff_index = 4;
    }

    for i in 5..n {
      if reader.query(1, 2, 3, i) == base {
        same_count += 1;
      } else {
        diff_count += 1;
        diff_index = i;
      }
    }

    let same_as_four_for_one = reader.query(0, 2, 3, 4) == base;
    if same_as_four_for_one == same_as_zero_for_four {
      same_count += 1;
    } else {
      diff_count += 1;
      diff_index = 1;
    }

    let same_as_four_for_two = reader.query(0, 1, 3, 4) == base;
    if same_as_four_for_two == same_as_zero_for_four {
      same_count += 1;
    } else {
      diff_count += 1;
      diff_index = 2;
    }

    let same_as_four_for_three = reader.query(0, 1, 2, 4) == base;
    if same_as_four_for_three == same_as_zero_for_four {
      same_count += 1;
    } else {
      diff_count += 1;
      diff_index = 3;
    }

    if same_count == diff_count {
      -1
    } else if same_count > diff_count {
      0
    } else {
      diff_index
    }
  }
}