8queen

#include <stdio.h>
#include <iostream.h>
#define QueenNum 8

void output(int solution[QueenNum])
{
for(int i=0;i<QueenNum;i++)
{
cout<<solution[i]<<" ";
}
cout<<"\n";
}

int judge(int solution[QueenNum])
{
for(int i=0;i<QueenNum;i++)
{
for(int j=0;j<QueenNum;j++)
{
if(solution[j] ==0)
{
cout<<"incomplete solution";
output(solution);
return 1;       //incomplete solution
}
else if(i != j && (solution[i] == solution[j] || solution[i]-solution[j] == i-j || solution[i]-solution[j] == j-i)  )
{
cout<<"Error\n";
return 0;       //Error solution
}
}
}
return 2;    //right solution

}

int main(void)
{
int solution[QueenNum];
int k = 0;
bool flag = false;
    for(int i=0;i<QueenNum;i++)
{
solution[i] = 0;

}
int test[QueenNum] = {2,4,3,1};
cout<<"====="<<judge(test);
while(k>=0)
{
while(solution[k]<QueenNum)
{
solution[k] = solution[k]+ 1;
if(judge(solution) == 2)
{
flag = true;
break;
}
else if(judge(solution) == 1)
{
k = k+1;
}
}
if(flag == true)           //find the solution and exit
{
cout<<"========Solution!===========";
output(solution);
break;
}
solution [k] = 0;
k = k-1;
}

return 0;
}

回溯法在纸上画出来是很容易的，但是在具体实现时，个人认为有两点要注意：
1. judge方法，判断solution是否为正解、不完全解或者错误解
2. 当判断为错误解时，怎么回溯，上面的代码里回溯应该是solution[k]已经从1遍历到4，若判断1~4都是错误解，那么就只能回溯到上一步，让solution[k]取solution[k]+1的值