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  • Triangular numbers

    http://codeforces.com/problemset/problem/47/A

    Triangular numbers
    time limit per test
    2 seconds
    memory limit per test
    256 megabytes
    input
    standard input
    output
    standard output

    A triangular number is the number of dots in an equilateral triangle uniformly filled with dots. For example, three dots can be arranged in a triangle; thus three is a triangular number. The n-th triangular number is the number of dots in a triangle with n dots on a side. . You can learn more about these numbers from Wikipedia (http://en.wikipedia.org/wiki/Triangular_number).

    Your task is to find out if a given integer is a triangular number.

    Input

    The first line contains the single number n (1 ≤ n ≤ 500) — the given integer.

    Output

    If the given integer is a triangular number output YES, otherwise output NO.

    Sample test(s)
    input
    1
    
    output
    YES
    
    input
    2
    
    output
    NO
    
    input
    3
    
    output
    YES
    

    用一个哈希表存储哪些是 triangular number,满足这个数字的要求就是这个数能由公式得到。
    AC代码:
    #include<iostream>
    #include<cstdio>
    #include<cstring>
    
    using namespace std;
    
    int p[200000];
    
    int main()
    {
        int n,i,x;
        memset(p,0,sizeof(p));
        for(i = 1; i <= 500; i++)
        {
            x = i*(i+1)/2;
            p[x] = 1;
        }
        while(scanf("%d",&n)!=EOF)
        {
            if(p[n] == 1)
            {
                printf("YES
    ");
            }
            else
            {
                printf("NO
    ");
            }
        }
    
        return 0;
    }
    


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  • 原文地址:https://www.cnblogs.com/keanuyaoo/p/3255915.html
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