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096 Su Doku -- v2.jl
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096 Su Doku -- v2.jl
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#!/usr/bin/julia
# Author: Trizen
# Date: 12 February 2024
# https://github.com/trizen
# https://projecteuler.net/problem=96
# Runtime: 1.023s
function is_valid(board, row, col, num)
# Check if the number is not present in the current row and column
for i in 1:9
if (board[row][i] == num) || (board[i][col] == num)
return false
end
end
# Check if the number is not present in the current 3x3 subgrid
start_row, start_col = 3*div(row-1, 3), 3*div(col-1, 3)
for i in 1:3, j in 1:3
if board[start_row + i][start_col + j] == num
return false
end
end
return true
end
function find_empty_locations(board)
positions = []
# Find all empty positions (cells with 0)
for i in 1:9, j in 1:9
if board[i][j] == 0
push!(positions, [i, j])
end
end
return positions
end
function find_empty_location(board)
# Find an empty positions (cell with 0)
for i in 1:9, j in 1:9
if board[i][j] == 0
return [i,j]
end
end
return (nothing, nothing)
end
function solve_sudoku_fallback(board)
row, col = find_empty_location(board)
if (row == nothing && col == nothing)
return true # Puzzle is solved
end
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 solve_sudoku_fallback(board)
return true
end
# If placing the current number doesn't lead to a solution, backtrack
board[row][col] = 0
end
end
return false # No solution found
end
function solve_sudoku(board)
while true
# Return early when the first 3 values are solved
if board[1][1] != 0 && board[1][2] != 0 && board[1][3] != 0
return board
end
empty_locations = find_empty_locations(board)
if length(empty_locations) == 0
break # it's solved
end
found = false
# Solve easy cases
for (i,j) in empty_locations
count = 0
value = 0
for n in 1:9
if is_valid(board, i, j, n)
count += 1
value = n
count > 1 && break
end
end
if count == 1
board[i][j] = value
found = true
end
end
found && continue
# Solve more complex cases
stats = Dict{String,Array}()
for (i,j) in empty_locations
arr = []
for n in 1:9
if is_valid(board, i, j, n)
append!(arr, n)
end
end
stats["$i $j"] = arr
end
cols = Dict{String,Int}()
rows = Dict{String,Int}()
subgrid = Dict{String,Int}()
for (i,j) in empty_locations
for v in stats["$i $j"]
k1 = "$j $v"
k2 = "$i $v"
k3 = join([3*div(i-1,3), 3*div(j-1,3), v], " ")
if !haskey(cols, k1)
cols[k1] = 1
else
cols[k1] += 1
end
if !haskey(rows, k2)
rows[k2] = 1
else
rows[k2] += 1
end
if !haskey(subgrid, k3)
subgrid[k3] = 1
else
subgrid[k3] += 1
end
end
end
for (i,j) in empty_locations
for v in stats["$i $j"]
if (cols["$j $v"] == 1 ||
rows["$i $v"] == 1 ||
subgrid[join([3*div(i-1,3), 3*div(j-1,3), v], " ")] == 1)
board[i][j] = v
found = true
end
end
end
found && continue
# Give up and try brute-force
solve_sudoku_fallback(board)
return board
end
return board
end
function euler_096()
fh = open("p096_sudoku.txt")
lines = filter((x)->occursin(r"^[0-9]+$",x), readlines(fh))
total = 0
while length(lines) > 0
rows = splice!(lines, 1:9)
grid = map((row) -> map((c)->parse(Int64, c), split(row, "")), rows)
solution = solve_sudoku(grid)
total += solution[1][1]*100 + solution[1][2]*10 + solution[1][3]
end
println(total)
end
euler_096()