Design a Number Container System

Tags : leetcode, hash, heap, set, cpp, medium

Problem Statement - link #

Design a number container system that can do the following:

Insert or Replace a number at the given index in the system.
Return the smallest index for the given number in the system.

Implement the NumberContainers class:

NumberContainers() Initializes the number container system.
void change(int index, int number) Fills the container at index with the number. If there is already a number at that index, replace it.
int find(int number) Returns the smallest index for the given number, or -1 if there is no index that is filled by number in the system.

Examples #

Example 1:

Input
["NumberContainers", "find", "change", "change", "change", "change", "find", "change", "find"]
[[], [10], [2, 10], [1, 10], [3, 10], [5, 10], [10], [1, 20], [10]]
Output
[null, -1, null, null, null, null, 1, null, 2]

Explanation
NumberContainers nc = new NumberContainers();
nc.find(10); // There is no index that is filled with number 10. Therefore, we return -1.
nc.change(2, 10); // Your container at index 2 will be filled with number 10.
nc.change(1, 10); // Your container at index 1 will be filled with number 10.
nc.change(3, 10); // Your container at index 3 will be filled with number 10.
nc.change(5, 10); // Your container at index 5 will be filled with number 10.
nc.find(10); // Number 10 is at the indices 1, 2, 3, and 5. Since the smallest index that is filled with 10 is 1, we return 1.
nc.change(1, 20); // Your container at index 1 will be filled with number 20. Note that index 1 was filled with 10 and then replaced with 20. 
nc.find(10); // Number 10 is at the indices 2, 3, and 5. The smallest index that is filled with 10 is 2. Therefore, we return 2.

Constraints #

1 <= index, number <= 10^9
At most 10^5 calls will be made to change and find.

Solutions #

class NumberContainers {
    unordered_map<int, int> map;
    unordered_map<int, set<int>>pam;
public:
    NumberContainers() {
    }
    
    void change(int index, int number) {
        if(map.find(index) != map.end()) {
            pam[map[index]].erase(index);
        }
        map[index] = number;
        pam[map[index]].insert(index);
    }
    
    int find(int number) {
        if(pam[number].empty()) {
            return -1;
        }
        auto it = pam[number].begin();
        return *it;
    }
};

/**
 * Your NumberContainers object will be instantiated and called as such:
 * NumberContainers* obj = new NumberContainers();
 * obj->change(index,number);
 * int param_2 = obj->find(number);
 */