Blue Bridge Cup 2015 Group B of the Sixth C language provincial tournament exercises solution to a problem - an array of nine points Exercises E.

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Blue Bridge Cup sixth C language group B match exercises Province

Problem E: an array of nine points

Test sites: the whole arrangement, backtracking, recursion

If on the recursive algorithm can be found in not very skilled Bowen algorithm a: recursively (including full array)

This code, test function a look that is truly the result of 1/3, and the function f is a look at a recursive call function, if the subject has done a lot of people to see that this is all arranged, because the loop from 0 9, and then swap to full permutation number k + 1 to 9, followed then swap back. So this question is not to say, I can see the details of the above recommended Bowen, the completed code is as follows:

#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);
		t=x[k]; x[k]=x[i]; x[i]=t; // 填空处
	}
}
	
int main()
{
	int x[] = {1,2,3,4,5,6,7,8,9};
	f(x,0);	
	return 0;
}

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