八皇后问题

#include <stdio.h>#include <stdlib.h>#define N 8 int column[N+1]; // 同栏是否有皇后，1表示有int rup[2*N+1]; // 右上至左下是否有皇后int lup[2*N+1]; // 左上至右下是否有皇后int queen[N+1] = {0};int num; // 解答编号void backtrack(int); // 递回求解int main(void) {    int i;    num = 0;     for(i = 1; i <= N; i++)        column[i] = 1;    for(i = 1; i <= 2*N; i++)        rup[i] = lup[i] = 1;    backtrack(1);        return 0;} void showAnswer() {    int x, y;    printf("\n解答 %d\n", ++num);    for(y = 1; y <= N; y++) {        for(x = 1; x <= N; x++) {            if(queen[y] == x) {                printf(" Q");            }            else {                printf(" .");            }        }        printf("\n");    }} void backtrack(int i) {    int j;     if(i > N){        showAnswer();    }    else {        for(j = 1; j <= N; j++) {            if(column[j] == 1 && rup[i+j] == 1 && lup[i-j+N] == 1) {               queen[i] = j;                // 设定为占用                column[j] = rup[i+j] = lup[i-j+N] = 0;                backtrack(i+1);                column[j] = rup[i+j] = lup[i-j+N] = 1;            }        }   }}