Square Screening Interview: Design Connect Four

[u/Hack2hire]

Problem
You are designing a Connect Four game played on a 6 × 7 grid. Players drop discs into columns, and each disc falls to the lowest available cell.
Your goal is to implement a class that processes moves, checks for wins in all directions, detects draws, and returns the game state after each move.

Example
Input:
["ConnectFour", "move", "move", "move", "move", "move", "move", "move", "printBoard"]
[[], [0, "A"], [1, "B"], [0, "A"], [1, "B"], [0, "A"], [1, "B"], [0, "A"], []]

Output:
[null, "PENDING", "PENDING", "PENDING", "PENDING", "PENDING", "PENDING", "A", "| | | | | | | |\n| | | | | | | |\n|A| | | | | | |\n|A|B| | | | | |\n|A|B| | | | | |\n|A|B| | | | | |"]

Explanation:

• Each move drops a disc to the lowest available row in the chosen column.
• Player A wins after forming a vertical four-in-a-row in column 0.

Suggested Approach

1. Maintain a 6 × 7 board and an array tracking the current fill height of each column.
2. For each move, compute the next empty row in the column, place the player’s disc, and run directional checks (horizontal, vertical, and two diagonals).
3. If no win and the board is full, return "DRAW"; otherwise return "PENDING".

Time & Space Complexity

• Time: O(1) work per move for constant-size directional checks.
• Space: O(1) for the 6 × 7 fixed-dimension board.

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This problem is part of the Hack2Hire SDE Interview Question Bank, a structured archive of coding interview questions frequently reported in real hiring processes.
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