XDU 1011

解法1:TLE

#include<stdio.h>
int main()
{
    long long n;
    //freopen("in.txt","r",stdin);
    while(scanf("%lld",&n)!=EOF){
        long long i=1,s=0;
        while(s<=n){
            s=i*i;
            i++;
        }
        if(i%2!=0)
            printf("odd\n");
        else
            printf("even\n");
    }
    return 0;
}

解法2:AC

#include<bits/stdc++.h>
using namespace std;
#define maxn 1e10 
long long sum(long long t)
{
    return t*(t+2); 
}
int main()
{
    long long n;
    //freopen("in.txt","r",stdin); 
    while(scanf("%lld",&n)!=EOF)
    {
        long long r=maxn,l=1,mid=(maxn+1)/2;
        while(1)
        {
            if(sum(mid)>n)
            {
                if(sum(mid-1)==n){
                    mid--;
                    break;
                }
                if(sum(mid-1)<n)
                    break;
                r=mid;
                mid=(l+r)/2;
            }
            else{
                if(sum(mid+1)>=n){
                    mid++;
                    break;
                }
                l=mid;
                mid=(l+r)/2;
            }
        }
        if(mid%2)
            printf("odd\n");
        else 
            printf("even\n");
    }
}