PAT 1069. The Black Hole of Numbers (stringstream)

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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 adigit.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;}

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