[Project Euler] Problem 30

Surprisingly there are only three numbers that can be written as the sum of fourth powers of their digits:

1634 = 1⁴ + 6⁴ + 3⁴ + 4⁴
8208 = 8⁴ + 2⁴ + 0⁴ + 8⁴
9474 = 9⁴ + 4⁴ + 7⁴ + 4⁴

As 1 = 1⁴ is not a sum it is not included.

The sum of these numbers is 1634 + 8208 + 9474 = 19316.

Find the sum of all the numbers that can be written as the sum of fifth powers of their digits.

这道题没有太多技巧可言，直接穷举法

由于9**5*7 < 1000000；所以满足条件的数不可能是7位或以上的数

我们从2穷举到 9**5*6；

#include <iostream>
#include <cmath>
usingnamespace std;

bool isGood(int);

int main(){
    int sum =0;
    for(int i=2; i<pow(9,5)*6; i++){
        if(isGood(i)){
            sum += i;
        }
    }
    cout << sum <<endl;
    
}

bool isGood(int num){
    int tmp =0;
    int backup = num;
    while(backup >0){
        tmp += pow(backup%10,5);
        backup /=10;
    }
    return tmp == num;
}