PAT 1069. The Black Hole of Numbers (stringstream)

可以用stringstream实现字符串和整型间的转换。

测试点5考察的是"Repeat in this manner we will soon end up at the number
6174 -- the "black hole" of 4-digit numbers."

我的理解是，输入若为6174, 则应输出 7641 - 1467 = 6174

#include <cstdio>
#include <algorithm>
#include <string>
#include <sstream>

using namespace std;

int n;

bool mycmp(const char a, const char b)
{
return a > b;
}

bool same_numbers(int n)
{
for (int i = 0; i < 10; ++ i)
{
if (n == 1111*i)
{
return true;
}
}
return false;
}

void print_steps(int b)
{
if (b == 6174)
{
printf("7641 - 1467 = 6174\n");
return ;
}

string digit;
stringstream ss;
int a;
while (b != 6174)
{
// get a
digit.clear();
ss.clear();
ss << b;
ss >> digit;
while (digit.size() < 4)
{
digit.push_back('0');
}
sort(digit.begin(), digit.end());
ss.clear();
ss << digit;
ss >> b;
sort(digit.begin(), digit.end(), mycmp);
ss.clear();
ss << digit;
ss >> a;
printf("%04d - %04d = %04d\n", a, b, a-b);
b = a - b;
}
}

int main()
{
scanf("%d", &n);

if ( same_numbers(n) )
{
printf("%04d - %04d = 0000\n", n, n);
} else
{
print_steps(n);
}

return 0;
}