Excel BI - Excel Challenge 766

excel-challenges

excel-formulas

🔰 Answer Expected Reverse the diagonals in 10x10 grid as shown.

Published

March 24, 2026

Illustration for Excel BI - Excel Challenge 766

Challenge Description

🔰 Answer Expected Reverse the diagonals in 10x10 grid as shown.

Solutions

library(tidyverse)
library(readxl)
library(matricks)

path = "Excel/700-799/766/766 Swap Diagonals.xlsx"
input = read_excel(path, range = "A2:J11", col_names = FALSE) %>% as.matrix()
test  = read_excel(path, range = "L2:U11", col_names = FALSE) %>% as.matrix()

swap_diagonals = function(mat) {
  n = nrow(mat)
  mat[cbind(1:n, 1:n)] = rev(mat[cbind(1:n, 1:n)])
  mat[cbind(1:n, n:1)] = rev(mat[cbind(1:n, n:1)])
  return(mat)
}

result = swap_diagonals(input)
all.equal(result, test)
#> [1] TRUE

Logic: Read the workbook ranges needed for the challenge.
Strengths: The code maps the workbook rule into a compact, reproducible pipeline.
Areas for Improvement: The solution assumes the workbook layout and selected ranges remain stable, so any structural change in the sheet would require small adjustments.
Gem: The elegant part is how little code is needed once the correct intermediate representation is chosen.

import numpy as np
import pandas as pd

path = "700-799/766/766 Swap Diagonals.xlsx"
input = pd.read_excel(path, header=None, usecols="A:J", skiprows=1, nrows=10).values
test  = pd.read_excel(path, header=None, usecols="L:U", skiprows=1, nrows=10).values

def swap_diagonals(mat):
    mat = mat.copy()
    n = mat.shape[0]
    idx = np.arange(n)
    mat[idx, idx] = mat[idx, idx][::-1]
    mat[idx, n-1-idx] = mat[idx, n-1-idx][::-1]
    return mat

result = swap_diagonals(input)
print(np.allclose(result, test)) # True

The Python version mirrors the same workbook logic with a concise, direct implementation.

Difficulty Level

Easy / Medium

The business rule is clear, though the workbook still needs a few transformation steps to reach the expected output.