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ProjectEuler_P12

Problem:

The sequence of triangle numbers is generated by adding the natural numbers. So the 7th triangle number would be 1 + 2 + 3 + 4 + 5 + 6 + 7 = 28. The first ten terms would be:

1, 3, 6, 10, 15, 21, 28, 36, 45, 55, ...

Let us list the factors of the first seven triangle numbers:

 1: 1
 3: 1,3
 6: 1,2,3,6
10: 1,2,5,10
15: 1,3,5,15
21: 1,3,7,21
28: 1,2,4,7,14,28

We can see that 28 is the first triangle number to have over five divisors.

What is the value of the first triangle number to have over five hundred divisors?

 

思路:

穷举,依次测试

 

C Code:

#include <stdio.h>
#include <math.h>

int DivisorCount(int n)
{
    int mid = (int)sqrt(n);
    int i = 0,count = 0;
    for(i = 1;i < mid ;i++)
    {
        if(0 == n%i)
        {
            count += 2;
        }
    }
    if(n == i*i)
    {
        count++;
    }
    else if(0 == n%i)
    {
        count += 2;
    }
    return count;
}

void main()
{
    int i = 1;
    for(i = 1;;i++)
    {
        int mul = i*(i+1)/2;
        if(500 <= DivisorCount(mul))
        {
            printf("%d %d\n",i,mul);
            break;
        }
    }
}

Result:

76576500