HackerRank - "Hexagonal Grid"

Interesting one.. It is more about data structure design actually. After you figure out how to represent cells, the DP formula will be very intuitive :)

Data structure: just interleave the 2 strings and form a bitset..

#include <cmath>
#include <cstdio>
#include <vector>
#include <string>
#include <iostream>
#include <algorithm>
#include <bitset>
using namespace std;

#define MAX_LEN 201

bool calc(int n, string &n1, string &n2)
{
    std::bitset<MAX_LEN> b;
    vector<bool> dp(2 * n, false);
    int last = 0;
    for (int i = 0; i < n; i++)
    {
        b[i * 2] = n1[i] - '0';
        if (!b[i * 2]) last = i * 2;
        b[i * 2 + 1] = n2[i] - '0';        
        if (!b[i * 2 + 1]) last = i * 2 + 1;
    }

    for (int i = 0; i < 2 * n; i++)
    {
        if (b[i])
        {
            dp[i] = (i == 0) ? true: dp[i - 1];
            continue;
        }
        // now b[i] is 0
        bool prev = (i == 0 ? true : (dp[i - 1]));
        if (!prev) continue;

        bool next = false, nnext = false;
        if (i < (2 * n - 1)) // 
        {
            next = b[i + 1];
            if (!next)
                dp[i + 1] = true;
        }
        if (i < (2 * n - 2))
        {
            nnext = b[i + 2];
            if (next && (!nnext))
                dp[i + 2] = true;
        }
    }
    return dp[last];
}

int main() 
{
    int t; cin >> t;
    while (t--)
    {
        int n; cin >> n;
        string n1, n2; cin >> n1 >> n2;
        bool r = calc(n, n1, n2);
        cout << (r ? "YES" : "NO") << endl;
    }
    return 0;
}