Counter II

Counter II - Problem

JavaScript Easy

Write a function createCounter that accepts an initial integer init and returns an object with three functions.

The three functions are:

increment() increases the current value by 1 and then returns it.
decrement() reduces the current value by 1 and then returns it.
reset() sets the current value to init and then returns it.

Input & Output

Example 1 — Basic Counter Operations

$ Input: init = 5, calls = ["increment", "increment", "decrement", "reset", "reset"]

› Output: [6,7,6,5,5]

💡 Note: Starting with 5: increment() → 6, increment() → 7, decrement() → 6, reset() → 5, reset() → 5

Example 2 — Starting from Zero

$ Input: init = 0, calls = ["increment", "increment", "decrement", "reset", "reset"]

› Output: [1,2,1,0,0]

💡 Note: Starting with 0: increment() → 1, increment() → 2, decrement() → 1, reset() → 0, reset() → 0

Example 3 — Negative Initial Value

$ Input: init = -2, calls = ["reset", "increment", "decrement"]

› Output: [-2,-1,-2]

💡 Note: Starting with -2: reset() → -2, increment() → -1, decrement() → -2

Constraints

-1000 ≤ init ≤ 1000
At most 1000 calls will be made to increment, decrement and reset

Visualization

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Asked in

G Google 15 f Facebook 12

The key insight is to use closures or classes to maintain state between function calls. The optimal approach uses JavaScript closures to encapsulate the initial and current values, returning an object with methods that operate on shared state. Time: O(1) per operation, Space: O(1) for state storage.

Common Approaches

✓ Class-Based Implementation

⏱️ Time: O(1) Space: O(1)

Create a class or object that maintains the initial value and current state, with methods that modify and return the current value. This provides clear separation of concerns.

Closure with Object Methods

⏱️ Time: O(1) Space: O(1)

Create a closure that captures the initial value and current value, then return an object with three methods that operate on the shared state.

Class-Based Implementation — Algorithm Steps

Define class with init and current properties
Implement increment, decrement, reset methods
Each method updates current and returns new value

Visualization

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Step-by-Step Walkthrough

Constructor

Create Counter object with init and current fields

Method Calls

Each method modifies the current field

State Tracking

Object preserves state between method invocations

Code -

solution.c — C

#include <stdio.h>
#include <stdlib.h>

typedef struct {
    int init;
    int current;
} Counter;

Counter* createCounter(int init) {
    Counter* counter = (Counter*)malloc(sizeof(Counter));
    counter->init = init;
    counter->current = init;
    return counter;
}

int increment(Counter* c) {
    return ++c->current;
}

int decrement(Counter* c) {
    return --c->current;
}

int reset(Counter* c) {
    c->current = c->init;
    return c->current;
}

Counter* solution(int init) {
    return createCounter(init);
}

int main() {
    int init;
    scanf("%d", &init);
    
    Counter* counter = solution(init);
    int result[5];
    result[0] = increment(counter);
    result[1] = increment(counter);
    result[2] = decrement(counter);
    result[3] = reset(counter);
    result[4] = reset(counter);
    
    printf("[");
    for (int i = 0; i < 5; i++) {
        printf("%d", result[i]);
        if (i < 4) printf(",");
    }
    printf("]\n");
    
    free(counter);
    return 0;
}

Time & Space Complexity

Time Complexity

⏱️

O(1)

All operations are simple arithmetic and assignment

✓ Linear Growth

Space Complexity

O(1)

Only stores two integer fields in the object

✓ Linear Space

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Input & Output

Constraints

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Common Approaches

Class-Based Implementation — Algorithm Steps

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Code -

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