#include <stdlib.h> #include <stdio.h> #define N 20 int nb_num; int tab[N]; int stack_ptr; int stack_op[N]; int stack_res[60]; int result; int find(int n, int i1, int a, int b, int op) { int i, j; int c; if (stack_ptr >= 0) { stack_res[3*stack_ptr] = a; stack_op[stack_ptr] = op; stack_res[3*stack_ptr+1] = b; stack_res[3*stack_ptr+2] = n; if (n == result) return 1; tab[i1] = n; } for(i=0;i<nb_num;i++) { for(j=i+1;j<nb_num;j++) { a = tab[i]; b = tab[j]; if (a != 0 && b != 0) { tab[j] = 0; stack_ptr++; if (find(a + b, i, a, b, '+')) return 1; if (find(a - b, i, a, b, '-')) return 1; if (find(b - a, i, b, a, '-')) return 1; if (find(a * b, i, a, b, '*')) return 1; if (b != 0) { c = a / b; if (find(c, i, a, b, '/')) return 1; } if (a != 0) { c = b / a; if (find(c, i, b, a, '/')) return 1; } stack_ptr--; tab[i] = a; tab[j] = b; } } } return 0; } int main(int argc, char **argv) { int i, res, p; if (argc < 3) { printf("usage: %s: result numbers...\n" "Try to find result from numbers with the 4 basic operations.\n", argv[0]); exit(1); } p = 1; result = atoi(argv[p]); printf("result=%d\n", result); nb_num = 0; for(i=p+1;i<argc;i++) { tab[nb_num++] = atoi(argv[i]); } stack_ptr = -1; res = find(0, 0, 0, 0, ' '); if (res) { for(i=0;i<=stack_ptr;i++) { printf("%d %c %d = %d\n", stack_res[3*i], stack_op[i], stack_res[3*i+1], stack_res[3*i+2]); } return 0; } else { printf("Impossible\n"); return 1; } }