#1582 - Special Positions in a Binary Matrix

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Problem Description

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 (rows and columns are 0-indexed).

Solution

/**
 * @param {number[][]} mat
 * @return {number}
 */
var numSpecial = function(mat) {
  const rows = mat.length;
  const cols = mat[0].length;
  const rowSums = new Array(rows).fill(0);
  const colSums = new Array(cols).fill(0);
  let result = 0;

  for (let i = 0; i < rows; i++) {
    for (let j = 0; j < cols; j++) {
      if (mat[i][j] === 1) {
        rowSums[i]++;
        colSums[j]++;
      }
    }
  }

  for (let i = 0; i < rows; i++) {
    for (let j = 0; j < cols; j++) {
      if (mat[i][j] === 1 && rowSums[i] === 1 && colSums[j] === 1) {
        result++;
      }
    }
  }

  return result;
};