LeetCode: Special Positions in a Binary Matrix Solution

Approach

Count number of 1s in each row, column

A special position is the position that

• has the value of 1
• number of 1s in its row and column are both 1

Implementation

1var numSpecial = function (mat) {
2  const [m, n] = [mat.length, mat[0].length]
3  const [numberOf1sInRow, numberOf1sInCol] = [
4    new Uint8Array(m),
5    new Uint8Array(n),
6  ]
7  let res = 0
8
9  for (let row = 0; row < m; row++) {
10    for (let col = 0; col < n; col++) {
11      if (mat[row][col]) {
12        numberOf1sInRow[row]++
13        numberOf1sInCol[col]++
14      }
15    }
16  }
17
18  for (let row = 0; row < m; row++) {
19    for (let col = 0; col < n; col++) {
20      res +=
21        mat[row][col] &&
22        numberOf1sInRow[row] === 1 &&
23        numberOf1sInCol[col] === 1
24      // boolean coerce to 1 if true, 0 if false
25    }
26  }
27
28  return res
29}

References

Original problem

Similar problems

N/A