八皇后－遞歸

重寫八皇后，最開始用雙層循環，而後用遞歸重寫，仍是遞歸易懂，優雅

 

  1 #include <stdio.h>
  2 #include <stdlib.h>
  3 #include <string.h>
  4 #include <math.h>
  5 #include "stack_seq_generic.h"
  6 
  7 #define QUEEN 4
  8 
  9 typedef struct{
 10     int x;
 11     int y;
 12 } Point;
 13 
 14 BOOL in_border(int x){
 15     if (x>=0 && x<QUEEN) {
 16         return TRUE;
 17     }
 18     return FALSE;
 19 }
 20 
 21 BOOL can_place(SqStack *s, Point *p){
 22     Point *top = (Point *)s->top;
 23     Point *base = (Point *)s->base;
 24     
 25     if (!in_border(p->x) || !in_border(p->y)) {
 26         return FALSE;
 27     }
 28     
 29     while (base < top) {
 30         int x_dif = abs(p->x - base->x);
 31         int y_dif = abs(p->y - base->y);
 32         
 33         if (base->y==p->y || x_dif==y_dif) {
 34             return FALSE;
 35         }
 36         base++;
 37     }
 38     return TRUE;
 39 }
 40 
 41 static int count = 0;
 42 
 43 void print_queens(SqStack *s){
 44     Point *top = s->top;
 45     Point *base = s->base;
 46     
 47     char area[QUEEN][QUEEN] = {0};
 48     memset(area, '*', sizeof(char)*QUEEN*QUEEN);
 49     
 50     if (top - base >= QUEEN) {
 51         while (base < top) {
 52             area[base->x][base->y] = '#';
 53             base++;
 54         }
 55         
 56         int i,j;
 57         for (i=0; i<QUEEN; i++) {
 58             for (j=0; j<QUEEN; j++) {
 59                 printf("%c ", area[i][j]);
 60             }
 61             printf("\n");
 62         }
 63         printf("\n");
 64         
 65         count++;
 66     }
 67     
 68 }
 69 
 70 void queens_recursion(SqStack *s, Point p){
 71     if (can_place(s, &p)) {
 72         push(s, &p);
 73         print_queens(s);
 74         Point next = {p.x+1, 0};
 75         queens_recursion(s, next);
 76     }else{
 77         if (stack_empty(s)) {
 78             return;
 79         }
 80         
 81         if (!in_border(p.y) || !in_border(p.x)){
 82             pop(s, &p);
 83             Point next = {p.x, p.y+1};
 84             queens_recursion(s, next);
 85         }else{
 86             Point next = {p.x, p.y+1};
 87             queens_recursion(s, next);
 88         }
 89         
 90     }
 91 }
 92 
 93 int main(void){
 94     SqStack stack;
 95     init_stack(&stack, sizeof(Point));
 96     
 97     //queens(&stack);
 98     Point p = {0, 0};
 99     queens_recursion(&stack, p);
100 
101     printf("total:%d\n", count);
102     
103     return 0;
104 }