Compact Object

Problem Statement

The task is to define a function that accepts an input in the form of an object or array, obj, and returns a new version of this object, termed a compact object. A compact object retains the structure and keys of the original object but omits any keys or indices associated with falsy values. Key points to note about falsy values are that these are values which, when evaluated in a Boolean context, yield false. These typically include false, 0, "" (empty string), null, undefined, and NaN.

This operation not only affects the top-level elements of obj but also its nested structures. Hence if obj is a deeply nested object, all levels will be subjected to this compacting process. Arrays are treated as objects too, where array indices act as object keys.

Since the input is assumed to result from JSON.parse, it will always be in the form of a valid JSON, which confines our values to numbers, strings, booleans, arrays, objects, null, but not functions or date objects.

Examples

Example 1

Input:

obj = [null, 0, false, 1]

Output:

[1]

Explanation:

All falsy values have been removed from the array.

Example 2

Input:

obj = {"a": null, "b": [false, 1]}

Output:

{"b": [1]}

Explanation:

obj["a"] and obj["b"][0] had falsy values and were removed.

Example 3

Input:

obj = [null, 0, 5, [0], [false, 16]]

Output:

[5, [], [16]]

Explanation:

obj[0], obj[1], obj[3][0], and obj[4][0] were falsy and removed.

Constraints

• obj is a valid JSON object
• 2 <= JSON.stringify(obj).length <= 106

Approach and Intuition

The steps to solve this problem can be broken into several clear phases:

1. Identify if the current item (either from object or array) is falsy. If yes, skip adding this to the result.

2. Check whether the item is an array or object:

   • If the element is an array or object, recursively process each element of the array or key-value pair in the object with the same conditional check for falsiness.

3. If the element is not falsy and not an object or array (i.e., it's a primary data type like string, number, boolean), directly add it to the resulting structure unless it's falsy.

For nested structures, the method recursively ensures that the check and removal of falsy values is applied thoroughly down to the deepest nested object or array. Finally, the cleaned structure, free from all falsy associated keys or indices, is returned.

Additional Insights:

• Handling of Empty Arrays and Objects: Post removal of falsy values, objects or arrays that become empty should be considered in the structural integrity of the output. For example, an object that had all falsy values should itself not appear if nested within another object or array.

• Performance Considerations: Given that the upper limit for the JSON string representation of the object can be quite large (up to 1,000,000 characters), the function's efficiency, particularly in terms of recursion depth and handling large nested structures efficiently, becomes paramount.

Overall, the process involves constructing a new version of the input by systematically removing undesired content while preserving the nested structure and essential content fidelity of the original obj.

Solutions

function simplifyStructure(data) {
    const dataStack = [[data, Array.isArray(data) ? [] : {}]];
    let simplifiedData = dataStack[0][1];

    while (dataStack.length > 0) {
        const [current, newCurrent] = dataStack.pop();

        for (const key in current) {
            const value = current[key];
            if (!value) continue;
            
            if (typeof value !== 'object') {
                Array.isArray(newCurrent) ? newCurrent.push(value) : newCurrent[key] = value;
                continue;
            }

            const newArrayOrObject = Array.isArray(value) ? [] : {};
            Array.isArray(newCurrent) ? newCurrent.push(newArrayOrObject) : newCurrent[key] = newArrayOrObject;
            dataStack.push([value, newArrayOrObject]);
        }
    }

    return simplifiedData;
}