Codefights

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Reverse On Diagonals

Description

The longest diagonals of a square matrix are defined as follows:

  • the first longest diagonal goes from the top left corner to the bottom right one;
  • the second longest diagonal goes from the top right corner to the bottom left one.

Given a square matrix, your task is to reverse the order of elements on both of its longest diagonals.

Example

For

matrix = [[1, 2, 3], [4, 5, 6], [7, 8, 9]]

the output should be

reverseOnDiagonals(matrix) = [[9, 2, 7], [4, 5, 6], [3, 8, 1]]

Input/Output

  • [execution time limit] 4 seconds (js)

  • [input] array.array.integer matrix

    Guaranteed constraints:
    1 ≤ matrix.length ≤ 100,
    matrix.length = matrix[i].length,
    1 ≤ matrix[i][j] ≤ 105.

  • [output] array.array.integer

    • Matrix with the order of elements on its longest diagonals reversed.

[JavaScript (ES6)] Syntax Tips

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// Prints help message to the console
// Returns a string
function helloWorld(name) {
console.log("This prints to the console when you Run Tests");
return "Hello, " + name;
}

Solution

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function reverseOnDiagonals(matrix) {
  var reversed = matrix.map((row) => row.slice());
  var n = matrix.length;
  for (var i = 0; i < n; i++) {
    reversed[i][i] = matrix[n - 1 - i][n - 1 - i];
    reversed[n - i - 1][i] = matrix[i][n - i - 1];
  }
  return reversed;
}