Special positions in a binary matrix

Array Matrix

68.8% acceptance

Feb 25, 2026

1514

Given an m x n binary matrix mat, return the number of special positions in mat. A position (i, j) is called special if mat[i][j] == 1 and all other elements in row i and column j are 0.

Solution

Rust

Time O(n²)

Space O(1)

LeetCode

solution.rs

impl Solution {
  pub fn num_special(mat: Vec<Vec<i32>>) -> i32 {
    let m = mat.len();
    let n = mat[0].len();
    let row_sum: Vec<i32> = mat.iter().map(|row| row.iter().sum()).collect();
    let col_sum: Vec<i32> = (0..n).map(|c| (0..m).map(|r| mat[r][c]).sum()).collect();
    let mut count = 0;
    for r in 0..m {
      for c in 0..n {
        if mat[r][c] == 1 && row_sum[r] == 1 && col_sum[c] == 1 {
          count += 1;
        }
      }
    }
    count
  }
}