The Weekly Challenge 335

The Strategy: Build a frequency map from the first word. For each subsequent word, update to the minimum count per character. Remove characters with zero count. The result repeats each remaining character by its minimum frequency.

sub common_characters {
    my (@words) = @_;
    return () if !@words;

    my %common;
    $common{$_}++ for split //, $words[0];

    for my $word ( @words[ 1 .. $#words ] ) {
        my %freq;
        $freq{$_}++ for split //, $word;
        for my $char ( keys %common ) {
            $common{$char} = exists $freq{$char}
              ? min( $common{$char}, $freq{$char} ) : 0;
        }
        delete @common{ grep { $common{$_} == 0 } keys %common };
    }

    my @result;
    for my $char ( sort keys %common ) {
        push @result, ($char) x $common{$char};
    }
    return @result;
}

from collections import Counter

def common_characters(words: list[str]) -> list[str]:
    """Characters common to all words, preserving multiplicity."""
    if not words:
        return []
    common = Counter(words[0])
    for word in words[1:]:
        freq = Counter(word)
        for ch in list(common):
            if ch in freq:
                common[ch] = min(common[ch], freq[ch])
            else:
                del common[ch]
    return sorted(common.elements())

The Strategy: Place moves on a 3x3 board, alternating players. After all moves, check all 8 lines (3 rows, 3 columns, 2 diagonals) for a winner. If a winner exists, return the player. If all 9 cells filled without a winner, return Draw. Otherwise Pending.

sub find_winner {
    my (@moves) = @_;
    my @board  = map { [ ('_') x 3 ] } 1 .. 3;
    my $player = 'A';
    for my $move (@moves) {
        my ( $row, $col ) = @$move;
        $board[$row][$col] = $player;
        $player = $player eq 'A' ? 'B' : 'A';
    }

    my $winner = _check_winner( \\@board );
    return $winner if $winner;
    return @moves == 9 ? 'Draw' : 'Pending';
}

def find_winner(moves: list[list[int]]) -> str:
    """Determine tic-tac-toe outcome from move sequence."""
    board = [["_"] * 3 for _ in range(3)]
    player = "A"
    for r, c in moves:
        board[r][c] = player
        player = "B" if player == "A" else "A"

    lines = []
    lines.extend(board)  # rows
    lines.extend([[board[r][c] for r in range(3)] for c in range(3)])  # cols
    lines.append([board[i][i] for i in range(3)])  # diag
    lines.append([board[i][2 - i] for i in range(3)])  # anti-diag

    for line in lines:
        if line[0] != "_" and line[0] == line[1] == line[2]:
            return line[0]
    return "Draw" if len(moves) == 9 else "Pending"