Ultraviolet A 10730

If there are no sub-sequences of three elements in the sequence that constitute an equal difference, the output is yes or no.

Mark the position where each number appears, and start from 0 to find the three-element arithmetic difference series. If the positions of the three elements meet the conditions, there is an arithmetic difference series in the original series.

#include<cstdio>#include<cstring>int n,num[10010];int main(){    int n;    while(scanf("%d",&n) == 1 && n)    {        getchar();        for(int i = 0; i < n; i++)        {            int a;            scanf("%d",&a);            num[a] = i;        }        int flag = 0;        for(int i = 0; i < n; i++)        {            for(int j = 1; 2*j+i < n; j++)            {                if(num[i] < num[i+j] && num[i+j] < num[i+2*j])                {                    flag = 1;                    puts("no");                }                else if(num[i] > num[i+j] && num[i+j] > num[i+2*j])                {                    flag = 1;                    puts("no");                }                if(flag)                    break;            }            if(flag)                break;        }        if(!flag)            puts("yes");    }    return 0;}