var exist = function(board, word) {
    var seen = [];
    var targetCharIdx = 0;
    var result = {
        found: false
    };
    existHelper(board, word, seen, result);
    return result.found;
};

var existHelper = function(board, word, seen, result) {

    if (word.length === seen.length) {
        if (wordMatches(word, seen, board)) {
            if (cellsAreUnique(seen)) {
                if (cellsAreAdjacent(seen)) {
                    result.found = true;
                }
            }
        }
    } else {
        for (var i = 0; i < board.length; i++) {
            for (var j = 0; j < board[0].length; j++) {
                seen.push([i, j])
                existHelper(board, word, seen, result)
                seen.pop();
            }
        }
    }
};

var cellsAreAdjacent = function(seen) {
    var i = 0;
    var j = 1;
    var cellOne;
    var cellTwo;

    while (j < seen.length) {
        cellOne = seen[i];
        cellTwo = seen[j];
        var diffOne = Math.abs(cellOne[0] - cellTwo[0]);
        var diffTwo = Math.abs(cellOne[1] - cellTwo[1]);
        if (!xor(diffOne === 1, diffTwo === 1)) {
            return false;
        }
        j += 1;
        i += 1;
    }
    return true;
};

var xor = function(option1, option2) {
    return ((option1 || option2) && !(option1 && option2));
};

var cellsAreUnique = function(seen) {
    var usedCoordinates = {};
    var lookup = '';

    for (var i = 0; i < seen.length; i++) {
        lookup = seen[i][0].toString() + seen[i][1].toString();

        if (usedCoordinates[lookup]) {
            return false;
        }
        usedCoordinates[lookup] = true;

    }
    return true;
};

var wordMatches = function(word, seen, board) {
    var constructedWord = '';

    seen.forEach(function(coordinate) {
        constructedWord += board[coordinate[0]][coordinate[1]];

    });

    return constructedWord === word;
};