Created
March 4, 2026 17:59
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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).
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| /** | |
| * @param {number[][]} mat | |
| * @return {number} | |
| */ | |
| var numSpecial = function(mat) { | |
| const m = mat.length; | |
| const n = mat[0].length; | |
| // Count how many 1s appear in each row | |
| const rowCount = new Array(m).fill(0); | |
| // Count how many 1s appear in each column | |
| const colCount = new Array(n).fill(0); | |
| // First pass: fill rowCount and colCount | |
| for (let i = 0; i < m; i++) { | |
| for (let j = 0; j < n; j++) { | |
| if (mat[i][j] === 1) { | |
| rowCount[i]++; | |
| colCount[j]++; | |
| } | |
| } | |
| } | |
| let specialCount = 0; | |
| // Second pass: check which 1s are special | |
| for (let i = 0; i < m; i++) { | |
| for (let j = 0; j < n; j++) { | |
| // A cell is special if: | |
| // - it's a 1 | |
| // - its row has exactly one 1 | |
| // - its column has exactly one 1 | |
| if (mat[i][j] === 1 && rowCount[i] === 1 && colCount[j] === 1) { | |
| specialCount++; | |
| } | |
| } | |
| } | |
| return specialCount; | |
| }; |
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