论数独解决

Question

有人可以帮我理解这个解决方案:

 Initialize 2D array with 81 empty grids (nx = 9, ny = 9)
 Fill in some empty grid with the known values
 Make an original copy of the array
 Start from top left grid (nx = 0, ny = 0), check if grid is empty
 if (grid is empty) {
   assign the empty grid with values (i)
   if (no numbers exists in same rows & same columns same as (i) & 3x3 zone (i) is currently in)
     fill in the number
   if (numbers exists in same rows & same columns same as (i) & 3x3 zone (i) is currently in)
     discard (i) and repick other values (i++)
 }
 else {
   while (nx < 9) {
     Proceed to next row grid(nx++, ny)
     if (nx equals 9) {
       reset nx = 1
       proceed to next column grid(nx,ny++)
       if (ny equals 9) {
         print solution
       }
     }
   }
 }

Answer 1

这是一个简单的蛮力解算器.它从左上角开始,逐行左右工作,尝试将每个可能的数字放入每个方块,然后继续使用递归调用.失败后,它会回溯并尝试不同的选择.

调用的函数通过检查已在行,列和框中放置了哪些值safe来确定将值n放在某个单元格中是否合法.

这是解决数独的最简单(也是最慢)的方法之一.