Ascending Cards - Google Top Interview Questions


Problem Statement :


You are given a list of integers cards, and are looking to order the cards in a way so that they are revealed in ascending order.

The cards are revealed in this manner: the top card is removed and revealed and then next card is moved to the back. This is repeated until there's no more cards.

Return an ordering of the cards such that they are revealed in ascending order.

Constraints

n ≤ 100,000 where n is the length of cards

Example 1

Input

cards = [1, 2, 3, 4, 5]

Output

[1, 5, 2, 4, 3]

Explanation
1 is removed and 5 is moved to the back, resulting in [2, 4, 3, 5].

2 is removed and 4 is moved to the back, resulting in [3, 5, 4]

3 is removed and 5 is moved to the back, resulting in [4, 5]

4 is removed and 5 is moved to the back, resulting in [5]

5 is removed and there's no more cards.


Solution :



title-img 




                        Solution in C++ :

int find(int u, vector<int> &root) {
    if (root[u] == u) return u;
    return root[u] = find(root[u], root);
}

void unite(int u, int v, vector<int> &root) {
    u = find(u, root);
    v = find(v, root);
    root[u] = v;
}

vector<int> solve(vector<int> &cards) {
    sort(cards.begin(), cards.end());
    int N = cards.size();
    vector<int> root(N);
    iota(root.begin(), root.end(), 0);
    vector<int> ret(N);

    int cur = 0;

    for (int i = 0; i < N; ++i) {
        ret[cur] = cards[i];
        unite(cur, (cur + 1) % N, root);
        cur = find((cur + 1) % N, root);
        cur = find((cur + 1) % N, root);
        /* if you want to combine the above 2 lines, replace with:
           cur = find((cur = find((cur + 1) % N, root) + 1) % N, root); */
    }

    return ret;
}
                    


                        Solution in Java :

import java.util.*;

class Solution {
    public int[] solve(int[] cards) {
        int n = cards.length;
        Arrays.sort(cards);

        int[] res = new int[n];
        Deque<Integer> dq = new LinkedList<>();
        for (int i = 0; i < n; i++) {
            dq.addLast(i);
        }

        int writeIdx = 0;
        for (int c : cards) {
            res[dq.pollFirst()] = c;
            dq.add(dq.pollFirst());
        }

        return res;
    }
}
                    


                        Solution in Python : 
                            
class Solution:
    def solve(self, cards):
        n = len(cards)
        # create another list where we simulate the game
        mapping = list(range(n))
        mapping = deque(mapping)
        res = [0] * n

        for card in sorted(cards):
            res[mapping[0]] = card
            mapping.popleft()
            if mapping:
                mapping.append(mapping.popleft())
        return res


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