Solved! Leetcode 950. Reveal Cards In Increasing Order

Description Reveal Cards In Increasing Order

You are given an integer array deck. There is a deck of cards where every card has a unique integer. The integer on the i^th card is deck[i].

You can order the deck in any order you want. Initially, all the cards start face down (unrevealed) in one deck.

You will do the following steps repeatedly until all cards are revealed:

Take the top card of the deck, reveal it, and take it out of the deck.
If there are still cards in the deck then put the next top card of the deck at the bottom of the deck.
If there are still unrevealed cards, go back to step 1. Otherwise, stop.

Return an ordering of the deck that would reveal the cards in increasing order.

Note that the first entry in the answer is considered to be the top of the deck.

Example 1

<strong>Input:</strong> deck = [17,13,11,2,3,5,7]
<strong>Output:</strong> [2,13,3,11,5,17,7]
<strong>Explanation:</strong> 
We get the deck in the order [17,13,11,2,3,5,7] (this order does not matter), and reorder it.
After reordering, the deck starts as [2,13,3,11,5,17,7], where 2 is the top of the deck.
We reveal 2, and move 13 to the bottom.  The deck is now [3,11,5,17,7,13].
We reveal 3, and move 11 to the bottom.  The deck is now [5,17,7,13,11].
We reveal 5, and move 17 to the bottom.  The deck is now [7,13,11,17].
We reveal 7, and move 13 to the bottom.  The deck is now [11,17,13].
We reveal 11, and move 17 to the bottom.  The deck is now [13,17].
We reveal 13, and move 17 to the bottom.  The deck is now [17].
We reveal 17.
Since all the cards revealed are in increasing order, the answer is correct.

Input: deck = [17,13,11,2,3,5,7]

Output: [2,13,3,11,5,17,7]

Explanation:

We get the deck in the order [17,13,11,2,3,5,7] (this order does not matter), and reorder it.

After reordering, the deck starts as [2,13,3,11,5,17,7], where 2 is the top of the deck.

We reveal 2, and move 13 to the bottom. The deck is now [3,11,5,17,7,13].

We reveal 3, and move 11 to the bottom. The deck is now [5,17,7,13,11].

We reveal 5, and move 17 to the bottom. The deck is now [7,13,11,17].

We reveal 7, and move 13 to the bottom. The deck is now [11,17,13].

We reveal 11, and move 17 to the bottom. The deck is now [13,17].

We reveal 13, and move 17 to the bottom. The deck is now [17].

We reveal 17.

Since all the cards revealed are in increasing order, the answer is correct.

Example 2

<strong>Input:</strong> deck = [1,1000]
<strong>Output:</strong> [1,1000]

1 2	<strong>Input:</strong> deck = [1,1000] <strong>Output:</strong> [1,1000]

Constraints

1 <= deck.length <= 1000
1 <= deck[i] <= 10⁶
All the values of deck are unique.

Solution

class Solution {
    public int[] deckRevealedIncreasing(int[] deck) {

        //let's simulate the rules 
        //find out the index which is going to get revelead in what order 
        //1. sort the deck
        Arrays.sort(deck);
        //2. initialize a deque
        ArrayDeque<Integer> dq = new ArrayDeque<>();
        for(int i=0;i<deck.length;i++){
            dq.addLast(i);
        }

        int[] res = new int[deck.length];
        int i = 0;
        //3. simulate the rules
        while(!dq.isEmpty()){
            res[i] = dq.pollFirst();
            i++;
            if(!dq.isEmpty()){
                dq.addLast(dq.pollFirst());
            }
        }
        //4. set the card value according to the order of revelation
        int[] ans  = new int[deck.length];
        for(int j=0;j<deck.length;j++){
            int idx = res[j];
            int num = deck[j];
            ans[idx] = num;
        }

        return ans;
    }
}

class Solution {

public int[] deckRevealedIncreasing(int[] deck) {

//let's simulate the rules

//find out the index which is going to get revelead in what order

//1. sort the deck

Arrays.sort(deck);

//2. initialize a deque

ArrayDeque<Integer> dq = new ArrayDeque<>();

for(int i=0;i<deck.length;i++){

dq.addLast(i);

}

int[] res = new int[deck.length];

int i = 0;

//3. simulate the rules

while(!dq.isEmpty()){

res[i] = dq.pollFirst();

i++;

if(!dq.isEmpty()){

dq.addLast(dq.pollFirst());

}

//4. set the card value according to the order of revelation

int[] ans = new int[deck.length];

for(int j=0;j<deck.length;j++){

int idx = res[j];

int num = deck[j];

ans[idx] = num;

}

return ans;

}

Time Complexity

Sort the deck: O(n logn)
Simulate the rules, with each iteration we are removing an element from the queue: O(n)
Iterating over the res array to populate the ans array: O(n)

Final: O(nlogn)

Space Complexity

res array: O(n)
ans array: O(n)

Final: O(n)

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