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096 Su Doku.sf
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096 Su Doku.sf
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#!/usr/bin/ruby
# Author: Trizen
# Date: 12 February 2024
# https://github.com/trizen
# https://projecteuler.net/problem=96
# Runtime: 31.915s
func is_valid(board, row, col, num) {
# Check if the number is not present in the current row and column
for i in ^9 {
if ((board[row][i] == num) || (board[i][col] == num)) {
return false
}
}
# Check if the number is not present in the current 3x3 subgrid
var (start_row, start_col) = (3*idiv(row, 3), 3*idiv(col, 3))
for i in ^3, j in ^3 {
if (board[start_row + i][start_col + j] == num) {
return false
}
}
return true
}
func find_empty_locations(board) {
var locations = []
# Find all empty positions (cells with 0)
for i in ^9, j in ^9 {
if (board[i][j] == 0) {
locations << [i, j]
}
}
return locations
}
func find_empty_location(board) {
# Find an empty position (cell with 0)
for i in ^9, j in ^9 {
if (board[i][j] == 0) {
return (i, j)
}
}
return (nil, nil) # If the board is filled
}
func solve_sudoku_fallback(board) {
var (row, col) = find_empty_location(board)
if (!defined(row) && !defined(col)) {
return true # Puzzle is solved
}
for num in (1..9) {
if (is_valid(board, row, col, num)) {
# Try placing the number
board[row][col] = num
# Recursively try to solve the rest of the puzzle
if (__FUNC__(board)) {
return true
}
# If placing the current number doesn't lead to a solution, backtrack
board[row][col] = 0
}
}
return false # No solution found
}
func solve_sudoku(board) {
loop {
# Return early when the first 3 values are solved
if ((board[0][0] != 0) && (board[0][1] != 0) && (board[0][2] != 0)) {
return board
}
var empty_locations = find_empty_locations(board) || break
var found = false
# Solve easy cases
for i,j in empty_locations {
var(count=0, value=0)
for n in (1..9) {
is_valid(board, i, j, n) || next
break if (++count > 1)
value = n
}
if (count == 1) {
board[i][j] = value
found ||= true
}
}
next if found
# Solve more complex cases
var stats = []
for i,j in empty_locations {
stats[i][j] = (1..9 -> grep{|n| is_valid(board, i, j, n) })
}
var cols = []
var rows = []
var subgrid = []
for i,j in empty_locations {
stats[i][j].each {|v|
cols[j][v] := 0 ++
rows[i][v] := 0 ++
subgrid[3*idiv(i,3)][3*idiv(j,3)][v] := 0 ++
}
}
for i,j in empty_locations {
stats[i][j].each {|v|
if ((cols[j][v] == 1) ||
(rows[i][v] == 1) ||
(subgrid[3*idiv(i,3)][3*idiv(j,3)][v] == 1)
) {
board[i][j] = v
found ||= true
}
}
}
next if found
# Give up and try brute-force
say "Fallback: #{empty_locations.len}"
solve_sudoku_fallback(board)
return board
}
return board
}
var grids = File(ARGV[0] \\ "p096_sudoku.txt").open_r.grep(/^[0-9]+$/)
var sum = 0
while (grids) {
var grid = grids.splice(0,9).map{ .chars.map{.to_i} }
var solution = solve_sudoku(grid)
sum += Num(join('', solution[0][0,1,2]))
}
say sum