LeetCode/1286_Iterator_for_Combination at master · KnowledgeCenterYoutube/LeetCode · GitHub

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Leetcode 1286: Iterator for Combination
Detailed video Explanation: https://youtu.be/LzYlG_p1-zs
===================================================

C++:
----
class CombinationIterator {
    string s;
    queue<string> q;

    void getCombination(int start, int length, string txt){
        if(length == 0){
            q.push(txt);
            return;
        }

        for(int i = start; i <= s.length() - length; ++i)
            getCombination(i+1, length-1, txt + s[i]);
    }
public:
    CombinationIterator(string characters, int combinationLength) {
        s = characters;
        string txt = "";
        getCombination(0, combinationLength, txt);
    }

    string next() {
        string str = q.front();
        q.pop();
        return str;
    }

    bool hasNext() {
        return !q.empty();
    }
};

/**
 * Your CombinationIterator object will be instantiated and called as such:
 * CombinationIterator* obj = new CombinationIterator(characters, combinationLength);
 * string param_1 = obj->next();
 * bool param_2 = obj->hasNext();
 */


Java:
-----
class CombinationIterator {
    private String s;
    Queue<String> q;

    private void getCombination(int start, int length, StringBuilder txt){
        if(length == 0){
            q.add(txt.toString());
            return;
        }

        for(int i = start; i <= s.length() - length; ++i){
            txt.append(s.charAt(i));
            getCombination(i+1, length-1, txt);
            txt.deleteCharAt(txt.length() - 1);
        }
    }
    public CombinationIterator(String characters, int combinationLength) {
        s = characters;
        q = new LinkedList();

        getCombination(0, combinationLength, new StringBuilder());
    }

    public String next() {
        return q.poll();
    }

    public boolean hasNext() {
        return !q.isEmpty();
    }
}

/**
 * Your CombinationIterator object will be instantiated and called as such:
 * CombinationIterator obj = new CombinationIterator(characters, combinationLength);
 * String param_1 = obj.next();
 * boolean param_2 = obj.hasNext();
 */


Python3:
--------
class CombinationIterator:

    def __init__(self, characters: str, combinationLength: int):
        self.q = []

        def getCombination(start, length, txt):
            if length == 0:
                self.q.append(txt)
                return

            for i in range(start, len(characters) - length + 1):
                getCombination(i+1, length-1, txt + characters[i])

        getCombination(0, combinationLength, "")

    def next(self) -> str:
        str = self.q[0]
        self.q.pop(0)
        return str

    def hasNext(self) -> bool:
        return len(self.q) > 0


# Your CombinationIterator object will be instantiated and called as such:
# obj = CombinationIterator(characters, combinationLength)
# param_1 = obj.next()
# param_2 = obj.hasNext()