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2015 蓝桥杯：5.九数组分数

15 分
对了

1,2,3…9 这九个数字组成一个分数，其值恰好为 1/3，如何组法？

下面的程序实现了该功能，请填写划线部分缺失的代码。

#include <stdio.h>

void test(int x[])
{
    int a = x[0]*1000 + x[1]*100 + x[2]*10 + x[3];
    int b = x[4]*10000 + x[5]*1000 + x[6]*100 + x[7]*10 + x[8];

    if(a*3==b) printf("%d / %d\n", a, b);
}
void f(int x[], int k)
{
    int i,t;
    if(k>=9){
        test(x);
        return;
    }

    for(i=k; i<9; i++){
        {t=x[k]; x[k]=x[i]; x[i]=t;}
        f(x,k+1);
        //_____________________________________________ // 填空处
        {t=x[k]; x[k]=x[i]; x[i]=t;}
    }
}

int main()
{
    int x[] = {1,2,3,4,5,6,7,8,9};
    f(x,0);
    return 0;
}