PAT_1038: Recover the Smallest Number

Given a collection of number segments, you are supposed to recover the smallest number from them. For example, given {32, 321, 3214, 0229, 87}, we can recover many numbers such like 32-321-3214-0229-87 or 0229-32-87-321-3214 with respect to different orders of combinations of these segments, and the smallest number is 0229-321-3214-32-87.

Input Specification:

Each input file contains one test case. Each case gives a positive integer N (<=10000) followed by N number segments. Each segment contains a non-negative integer of no more than 8 digits. All the numbers in a line are separated by a space.

Output Specification:

For each test case, print the smallest number in one line. Do not output leading zeros.

Sample Input:

5 32 321 3214 0229 87
      

Sample Output:

22932132143287      

備注：思路是将字元串排序，排序的比較規則是：兩個字元串m和n，比較拼接起來的兩個數mn和nm誰更小。另外要注意一些邊界條件判斷，例如所有的輸入都為0，這時要輸出一個0為最終結果。      

程式的細節點是字元串指針數組的qsort寫法，第三個參數是sizeof（char *），是以傳遞給比較函數compare的參數就是指針的指針，即char **。      

#include<stdio.h>
#include<string.h>
#include<stdlib.h>

const int MAXSIZE = 10;
const int MAXNUM = 10005;

int compare(const void *a, const void *b)
{
	char *s1 = *(char **)a;
	char *s2 = *(char **)b;

	char tmp1[MAXSIZE*2+1];
	char tmp2[MAXSIZE*2+1];

	// s1s2
	strcpy(tmp1,s1);
	strcat(tmp1,s2);
	// s2s1
	strcpy(tmp2,s2);
	strcat(tmp2,s1);

	return strcmp(tmp1,tmp2);
}

bool IsAllZeros(char *s)
{
	for(int i=0;s[i]!='\0';i++)
	{
		if(s[i]!='0')
			return false;
	}
	return true;
}

int main()
{
	int n,i;
	bool endofzeros = false;
	char *s_list[MAXNUM];
	scanf("%d",&n);

	for(i=0;i<n;i++)
	{
		s_list[i] = new char[MAXSIZE];
		scanf("%s",s_list[i]);
	}

	qsort(s_list,n,sizeof(char *),compare);

	for(i=0;i<n;i++)
	{
		if(!IsAllZeros(s_list[i]))
			break;
	}
	if(i==n)
	{
		printf("0");
		return 0;
	}
	for(int j=i;j<n;j++)
	{
		// omit the leading zeros
		if(j==i)
		{
			for(int k=0;s_list[j][k]!='\0';k++)
			{
				if(endofzeros)
					printf("%c",s_list[j][k]);
				else if(!endofzeros && s_list[j][k]!='0')
				{
					endofzeros = true;
					printf("%c",s_list[j][k]);
				}
			}
		}
		else
			printf("%s",s_list[j]);
	}
	return 0;
}