Problems › JavaScript › patterns
Total the two diagonals
A scoring sheet is a square grid, and the bonus is whatever sits on the two diagonals.
- The grid is square.
- Add every cell on the top-left to bottom-right diagonal, and every cell on the other one.
- On an odd-sized grid the centre belongs to both diagonals, and is counted once.
- An empty grid totals zero.
diagonalTotal(sheet: list<list<int>>) → int
Where you start
function diagonalTotal(sheet) {
}Worked examples
| Call | Result |
|---|---|
diagonalTotal([[1,2,3],[4,5,6],[7,8,9]]) | 25 |
diagonalTotal([[1,2],[3,4]]) | 10 |
diagonalTotal([[5]]) | 5 |
diagonalTotal([]) | 0 |
Hint
Walk one index down the grid. At row i the two diagonal cells are column i and column (last - i) — and on an odd grid those meet in the middle.
Reference solution in JavaScript
function diagonalTotal(sheet) {
let total = 0;
const n = sheet.length;
for (let i = 0; i < n; i += 1) {
total += sheet[i][i];
if (i !== n - 1 - i) total += sheet[i][n - 1 - i];
}
return total;
}