There is a number puzzle which appears in the daily paper. Because I'm between Python projects, I thought it might be fun to write a program to solve it....20 minute job, max.
On closer inspection, it became apparent that it's not a simple thing to program. How would you approach it? The puzzle: a 4 x 4 grid. The rows are summed (and given), the cols are summed (and given), and the two diagonals are summed, and given. In addition, 4 clues are given, but none of the 4 are in the same row or col. Example from today's paper:...solution time is 8 minutes, 1 second, so they say. The set of allowable numbers is 1 thru 9 Rows: 3 + B + C + D = 22 E + F + 8 + H = 26 I + J + K + 8 = 31 M + 7 + O + P = 25 Col sums: 24, 18, 31, 31 Diag sums: 3 + F + K + P = 24 M + J + 8 + D = 24 The first impulse is to just brute force it with nested for loops, but the calculator shows the possible combinations are 9^12 = 5,159,780,352, which would take much too long. Another approach would be to inspect each square and determine what the range of reasonable numbers would be. For example, if A + 9 + C + D = 14, then A, C, D can only have a value of 1 or 2 or 3, which would greatly reduce the for loop range of A, C and D. While useful, it's still a manual task. I can't help but think there's a better way. If you have a real Python project, this isn't worth your time, but if a student, it might be a good exercise to think how you'd do it. Norm B -- http://mail.python.org/mailman/listinfo/python-list
