The problem is already stated in the topic name. I have KMP values and I need to recover Z function values and vice versa. Thank you!

Let's assume we have declared integer variables a and b somewhere in the program. The following pieces of code behave identically.

1.

a = 1;
b = 1;

2.

a = b = 1;

However, is there any C++ code convention (Google C++ Style Guide didn't give me an answer) that tells us in which way to write?

It is a well-known task to answer whether a node is an ancestor to another one with time complexity O(n) for preprocessing and O(1) for a query.

Each time you enter the node in recursive function DFS, you increase the time counter by one and call it an "entrance" time, and after recursively processing its sons, you increase the time counter by one and call it an "exit" time. Here is the pseudocode.

DFS(u, p): // u is the current node, p is its parent
    increase the timer counter
    in[u] = timer
    for all (u, v) in edges:
        if v != p:
            DFS(v, u)
    increase the timer counter
    out[u] = timer

Now u is an ancestor of v .

Is there someway to implement the same algorithm but with non-recursive DFS?

There is a line l given by the equation ax + by + c = 0 and the point P(x₀, y₀). Let Q(x₁, y₁) be projection of P on l. Am I right that ?

I really liked the previous year's post on IOI participants so I decided to do the same for this year.

UPD: Colors updated

If you know any other countries' delegations, let me know in the comments. Thanks!

Has anyone ever got problems because of forgetting to initialize a global variable?

And should I always initialize a variable when I create it?

P.S. I am talking about C++. Are the global variables initialized with "zero" by default? Or it depends on the compiler?

#include <iostream>
#include <cstring>
#include <algorithm>
#include <string>
#define MX 1000005
using namespace std;

struct BN
{
    int siz, num[MX];
    BN()
    {
        siz = 1;
        memset(num, 0, sizeof(num));
    }
    BN(string &a)
    {
        siz = a.size();
        memset(num, 0, sizeof(num));
        for (int i = 0; i < a.size(); i++)
            num[i] = a[a.size() - i - 1] - '0';
    }
    void len()
    {
        siz = MX - 1;
        while (siz > 0 && num[siz] == 0)
            siz--;
        siz++;
    }
    void inc()
    {
        num[0]++;
        for (int i = 0; i < MX - 1; i++)
        {
            num[i + 1] += num[i] / 10;
            num[i] %= 10;
        }
        len();
    }
    string tostring()
    {
        string a;
        for (int i = siz - 1; i >= 0; i--)
            a += (char)(num[i] + '0');
        return a;
    }
};

BN w;
string s, t, u, v, v1;

string sol()
{
    if (s.size() % 2 == 1)
    {
        u = s.substr(0, s.size() / 2 + 1);
        v = u;
        reverse(v.begin(), v.end());
        v = u + v.substr(1);
        if (v <= s)
        {
            w = BN(u);
            w.inc();
            u = w.tostring();
            v = u;
            reverse(v.begin(), v.end());
            v = u + v.substr(1);
        }
        u = s.substr(0, s.size() / 2);
        v1 = u;
        reverse(v1.begin(), v1.end());
        v1 = u + s[s.size() / 2] + v1;
        if (v1 <= s)
        {
            w = BN(u);
            w.inc();
            u = w.tostring();
            v1 = u;
            reverse(v1.begin(), v1.end());
            v1 = u + s[s.size() / 2] + v1;
        }
        if (v < v1)
            return v;
        return v1;
    }
    u = s.substr(0, s.size() / 2);
    v = u;
    reverse(v.begin(), v.end());
    v = u + v;
    if (v <= s)
    {
        w = BN(u);
        w.inc();
        u = w.tostring();
        v = u;
        reverse(v.begin(), v.end());
        v = u + v;
    }
    return v;
}

int main()
{
    int n;
    cin >> n;
    for (int i = 0; i < n; i++)
    {
        cin >> s;
        t = sol();
        cout << t << "\n";
    }
}

Actually I do have a solution for this problem (maybe it is not correct but I didn't create a post for helping with solution). But I wonder why each time I call sol(), the program crashes and gives SIGSEGV.

Can anyone explain?

P.S. BN is a big number structure. Used it to increase a big number by one.

Given a weighted digraph with weights either 0 or 1 find the shortest path. I heard that it can be solved using BFS and deque. But I don't really know how to prevent an vertex from appearing in the deque several times. Which condition on adding them to deque should I add? Thanks.