1019 数字黑洞

部分正确。 测试点2，3错误。

反复找不到原因，后来和别人的对比了一下，N不用字符串，直接当成整数处理。 

//1019数字黑洞

#include<iostream>
#include<string>
#include<stdio.h>
#include<algorithm>
using namespace std;
int main()
{
  string N;
  cin >> N;
  int a[4];
  int x = 0, y = 0;
  int result = -1;
  for (int i = 0; i < N.length(); i++) {
    a[i] = N[i] - '0';
  }

  while (result != 6174 && result !=0) {
    sort(a, a+4);
    y = (a[0] * 1000 + a[1] * 100 + a[2] * 10 + a[3]);
    x = (a[3] * 1000 + a[2] * 100 + a[1] * 10 + a[0]);
    result = x - y;
    printf("%04d - %04d = %04d\n",x,y,result);
    a[0] = result / 1000;
    a[1] = (result / 100) % 10;
    a[2] = (result / 10) % 10;
    a[3] = result % 10;
  }
  return 0;
}

 后来改了一下，（N不用字符串，直接当成整数处理）。测试通过。

#include<stdio.h>
#include<algorithm>
int splitN(int N, int*a) {
  a[0] = N / 1000;
  a[1] = (N / 100) % 10;
  a[2] = (N / 10) % 10;
  a[3] = N % 10;
}
int main()
{
  int  N;
  scanf("%d",&N);
  int a[4];
  int x = 0, y = 0;
  int result = -1;
  splitN(N, a);
  do {
    std::sort(a, a + 4);
    y = (a[0] * 1000 + a[1] * 100 + a[2] * 10 + a[3]);
    x = (a[3] * 1000 + a[2] * 100 + a[1] * 10 + a[0]);
    result = x - y;
    printf("%04d - %04d = %04d\n", x, y, result);
    splitN(result, a);
  } while (result != 6174 && result != 0);
  return 0;
}