Testing Round 19 (Div. 3)

A

模拟即可。

#include <bits/stdc++.h>
using namespace std;
#define int long long
using ll = long long;
const int M = 1234567890;
const int mod = 998244353;
void Totoro()
{
int n;
cin>>n;
vector<int>a(n+1);
ll sum=0;
for(int i=1;i<=n;i++)
{
cin>>a[i];
if(i&1)
{
    sum+=a[i];
    continue;
}
sum-=a[i];
}
cout<<sum<<'\n';
}
signed main()
{
    int t = 1;
    cin>>t;
    while (t--)
    {
        Totoro();
    }
}

jiangly-

#include <bits/stdc++.h>

using i64 = long long;

void solve() {
    int n;
    std::cin >> n;

    std::vector<int> a(n);
    for (int i = 0; i < n; i++) {
        std::cin >> a[i];
    }

    int ans = 0;
    for (int i = 0; i < n; i++) {
        if (i % 2 == 0) {
            ans += a[i];
        } else {
            ans -= a[i];
        }
    }
    std::cout << ans << "\n";
}

int main() {
    std::ios::sync_with_stdio(false);
    std::cin.tie(nullptr);

    int t;
    std::cin >> t;

    while (t--) {
        solve();
    }

    return 0;
}

B

模拟即可。

#include <bits/stdc++.h>
using namespace std;
#define int long long
using ll = long long;
const int M = 1234567890;
const int mod = 998244353;
int mp[4];
void Totoro()
{

    int a,b;
    cin>>a>>b;
    mp[a]++;
    mp[b]++;
    for(int i=1;i<=3;i++)
    {
        if(!mp[i])
        {
            cout<<i<<'\n';
            return;
        }
    }
}
signed main()
{
    int t = 1;
    while (t--)
    {
        Totoro();
    }
}

jiangly

这个太优雅了，由于 1，2，3 异或起来是 0，一个没来相当于就是他的异或，巧妙。

#include <bits/stdc++.h>

using i64 = long long;

int main() {
    std::ios::sync_with_stdio(false);
    std::cin.tie(nullptr);

    int a, b;
    std::cin >> a >> b;

    std::cout << (a ^ b) << "\n";

    return 0;
}

C1

暴力即可。

#include <bits/stdc++.h>
using namespace std;
#define int long long
using ll = long long;

void Totoro()
{
    string s;
    cin >> s;
    int n = s.size();
    for (int i = 1; i < n; i++)
    {
        if (i * 2 <= n)
            continue;
        string t = s.substr(0, i);
        if (t == s.substr(n - i, i))
        {
            cout << "YES\n"
                 << t << "\n";
            return;
        }
    }
    cout << "NO\n";
}
signed main()
{
    int t = 1;
    while (t--)
    {
        Totoro();
    }
}

jiangly

直接用 kmp 了，甚至没写暴力。

#include <bits/stdc++.h>

using i64 = long long;

int main() {
    std::ios::sync_with_stdio(false);
    std::cin.tie(nullptr);

    std::string s;
    std::cin >> s;

    int n = s.size();
    std::vector<int> f(n + 1);
    for (int i = 1, j = 0; i < n; i++) {
        while (j > 0 && s[i] != s[j]) {
            j = f[j];
        }
        j += (s[i] == s[j]);
        f[i + 1] = j;
    }

    if (f[n] > n / 2) {
        std::cout << "YES\n";
        std::cout << s.substr(0, f[n]) << "\n";
    } else {
        std::cout << "NO\n";
    }

    return 0;
}

C2

KMP。思考 next 数组的含义。

#include <bits/stdc++.h>
using namespace std;
#define int long long
using ll = long long;
vector<int> prefix_function(const string &s)
{
    int n = s.size();
    vector<int> pi(n);
    for (int i = 1, j; i < n; i++)
    {
        j = pi[i - 1];
        while (j > 0 and s[i] != s[j])
            j = pi[j - 1];
        if (s[i] == s[j])
            j++;
        pi[i] = j;
    }
    return pi;
}

void Totoro()
{
    string s;
    cin >> s;
    int n = s.size();
    vector<int> pi = prefix_function(s);
    if (pi[n - 1] * 2 > n)
    {
        cout << "YES\n"
             << s.substr(0, pi[n - 1]) << "\n";
    }
    else
    {
        cout << "NO\n";
    }
}
signed main()
{
    int t = 1;
    while (t--)
    {
        Totoro();
    }
}