Flip columns for maximum number of equal rows

Array Hash Table Matrix

78.6% acceptance

Feb 25, 2026

1344

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You are given an m x n binary matrix matrix. You can choose any number of columns in the matrix and flip every cell in that column (i.e., Change the value of the cell from 0 to 1 or vice versa). Return the maximum number of rows that have all values equal after some number of flips.

Solution

Rust

Time O(n)

Space O(n)

LeetCode

solution.rs

impl Solution {
  pub fn max_equal_rows_after_flips(matrix: Vec<Vec<i32>>) -> i32 {
    let mut count: std::collections::HashMap<Vec<i32>, i32> = std::collections::HashMap::new();
    for row in &matrix {
      let key: Vec<i32> = row.iter().map(|&v| v ^ row[0]).collect();
      *count.entry(key).or_insert(0) += 1;
    }
    *count.values().max().unwrap_or(&0)
  }
}