NumberContainerSystem.txt

class NumberContainers {
    // Map to store index -> number mapping
    private Map<Integer, Integer> indexToNum;
    // Map to store number -> TreeSet of indices mapping
    private Map<Integer, TreeSet<Integer>> numToIndices;
    
    public NumberContainers() {
        indexToNum = new HashMap<>();
        numToIndices = new HashMap<>();
    }
    
    public void change(int index, int number) {
        // If index already contains a number, remove it from old number's indices
        if (indexToNum.containsKey(index)) {
            int oldNum = indexToNum.get(index);
            numToIndices.get(oldNum).remove(index);
            // If no more indices for this number, remove the entry
            if (numToIndices.get(oldNum).isEmpty()) {
                numToIndices.remove(oldNum);
            }
        }
        
        // Update index -> number mapping
        indexToNum.put(index, number);
        
        // Update number -> indices mapping
        numToIndices.computeIfAbsent(number, k -> new TreeSet<>()).add(index);
    }
    
    public int find(int number) {
        // If number exists in the system, return its smallest index
        if (numToIndices.containsKey(number) && !numToIndices.get(number).isEmpty()) {
            return numToIndices.get(number).first();
        }
        return -1;
    }

    // Test method
    public static void main(String[] args) {
        NumberContainers nc = new NumberContainers();
        
        // Test case from example
        System.out.println(nc.find(10));  // Expected: -1
        nc.change(2, 10);
        nc.change(1, 10);
        nc.change(3, 10);
        nc.change(5, 10);
        System.out.println(nc.find(10));  // Expected: 1
        nc.change(1, 20);
        System.out.println(nc.find(10));  // Expected: 2
        
        // Additional test cases
        NumberContainers nc2 = new NumberContainers();
        nc2.change(1, 10);
        System.out.println(nc2.find(10));  // Expected: 1
        nc2.change(1, 20);
        System.out.println(nc2.find(10));  // Expected: -1
        System.out.println(nc2.find(20));  // Expected: 1
    }
}