Codeforces 1462A Favorite Sequence

题意

给一个数组$b$，形如$a_1,a_3,…,a_4,a_2$，要求还原出$a$数组。

分析

看$b$数组里奇数项是从左往右，偶数项是从右往左，维护一个左指针$l$，一个右指针$r$模拟即可。

#pragma GCC optimize(3, "Ofast", "inline")

#include <bits/stdc++.h>

#define start ios::sync_with_stdio(false);cin.tie(0);cout.tie(0);
#define ll long long
#define ull unsigned long long
#define int ll
#define ls st<<1
#define rs st<<1|1
#define pii pair<int,int>
#define rep(z, x, y) for(int z=x;z<=y;++z)
#define repd(z, x, y) for(int z=x;z>=y;--z)
#define com bool operator<(const node &b)const
using namespace std;
mt19937 rnd(chrono::high_resolution_clock::now().time_since_epoch().count());
const int maxn = (ll) 1e6 + 5;
const int mod = 998244353;
const int inf = 0x3f3f3f3f;
int T = 1;
int a[maxn];

void solve() {
    int n;
    cin >> n;
    rep(i, 1, n)cin >> a[i];
    int l = 1, r = n;
    rep(i, 1, n) {
        if (i & 1)
            cout << a[l++] << ' ';
        else
            cout << a[r--] << ' ';
    }
    cout << '\n';
}

signed main() {
    start;
    cin >> T;
    while (T--)
        solve();
    return 0;
}