luogu P2757 [国家集训队]等差子序列

题目链接

luogu P2757 [国家集训队]等差子序列

题解

线段树好题

我选择暴力

代码

// luogu-judger-enable-o2
#include<cstdio>
inline int read() {
    int x = 0,f = 1;
    char c = getchar();
    while(c < '0' || c > '9')c = getchar();
    while(c <= '9' && c >= '0') x = x * 10 + c - '0',c = getchar();
    return x * f;
}
const int maxn = 10007;
int a[maxn],b[maxn];
int main() {
    int t = read();
    int n;
    while(t --) {
        n = read(); bool flag = false;
        for(int i = 1;i <= n;++ i) a[i] = read(),b[a[i]] = i;
        for(int i = 1;i <= n;++ i) {
            for(int j = 1;j <= n;++ j) {
                int k = a[i];
                if(k + j + j <= n) if(b[k + j] > i && b[k + j + j] > b[k + j]) {flag = true;break;}
                if(k - j - j > 0)  if(b[k - j] > i && b[k - j - j] > b[k - j]) {flag = true;break;}
            }
            if(flag) break;
        }
        if(flag) puts("Y");
        else puts("N");
        for(int i = 1;i <= n;++ i) b[i] = 0;
    }
    return 0;
}