Letter Tile Possibilities

Problem statement

You have n  tiles, where each tile has one letter tiles[i] printed on it.

Return the number of possible non-empty sequences of letters you can make using the letters printed on those tiles.

Example 1:

Input: tiles = "AAB"Output: 8Explanation: The possible sequences are "A", "B", "AA", "AB", "BA", "AAB", "ABA", "BAA".

Example 2:

Input: tiles = "AAABBC"Output: 188

Example 3:

Input: tiles = "V"Output: 1

Constraints:

• 1 <= tiles.length <= 7
• tiles consists of uppercase English letters.

My solution

/**
 * @param {string} tiles
 * @return {number}
 */
var numTilePossibilities = function(tiles) {
    if (!tiles.length) {
        return 0;
    }
    
    let count = 0;
    let tracker = new Set();
    
    // console.log(tiles)
    
    for (let i = 0; i < tiles.length; i++) {
        const char = tiles.charAt(i)
        
        if (tracker.has(char)) {
            continue;
        }
        
        // console.log(">>>", tiles.slice(0, i) + tiles.slice(i + 1), i)
        
        count += numTilePossibilities(tiles.slice(0, i) + tiles.slice(i + 1)) + 1
        
        tracker.add(char)
    }
    
    return count;
};