Problem

Given two values o1 and o2, return a boolean value indicating whether two values, o1 and o2, are deeply equal.

For two values to be deeply equal , the following conditions must be met:

  • If both values are primitive types, they are deeply equal if they pass the === equality check.

  • If both values are arrays, they are deeply equal if they have the same elements in the same order, and each element is also deeply equal according to these conditions.

  • If both values are objects, they are deeply equal if they have the same keys, and the associated values for each key are also deeply equal according to these conditions.

You may assume both values are the output of JSON.parse. In other words, they are valid JSON.

Please solve it without using lodash’s _.isEqual() function

Examples

Example 1:

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Input: o1 = {"x":1,"y":2}, o2 = {"x":1,"y":2}
Output: true
Explanation: The keys and values match exactly.

Example 2:

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Input: o1 = {"y":2,"x":1}, o2 = {"x":1,"y":2}
Output: true
Explanation: Although the keys are in a different order, they still match exactly.

Example 3:

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Input: o1 = {"x":null,"L":[1,2,3]}, o2 = {"x":null,"L":["1","2","3"]}
Output: false
Explanation: The array of numbers is different from the array of strings.

Example 4:

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Input: o1 = true, o2 = false
Output: false
Explanation: true !== false

Constraints:

  • 1 <= JSON.stringify(o1).length <= 10^5
  • 1 <= JSON.stringify(o2).length <= 10^5
  • maxNestingDepth <= 1000

Solution

Method 1 – Recursive Deep Comparison

Intuition

Recursively compare primitives, arrays, and objects according to the deep equality rules. For objects, compare keys and values; for arrays, compare length and each element.

Approach

  1. If both are primitives, compare with ===.
  2. If both are arrays, check length and recursively compare each element.
  3. If both are objects, check keys and recursively compare values for each key.
  4. Otherwise, return false.

Code

JavaScript
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function deepEqual(o1, o2) {
    if (o1 === o2) return true;
    if (typeof o1 !== typeof o2) return false;
    if (o1 === null || o2 === null) return o1 === o2;
    if (Array.isArray(o1) && Array.isArray(o2)) {
        if (o1.length !== o2.length) return false;
        for (let i = 0; i < o1.length; ++i) {
            if (!deepEqual(o1[i], o2[i])) return false;
        }
        return true;
    }
    if (typeof o1 === 'object' && typeof o2 === 'object') {
        const k1 = Object.keys(o1), k2 = Object.keys(o2);
        if (k1.length !== k2.length) return false;
        k1.sort(); k2.sort();
        for (let i = 0; i < k1.length; ++i) {
            if (k1[i] !== k2[i]) return false;
            if (!deepEqual(o1[k1[i]], o2[k2[i]])) return false;
        }
        return true;
    }
    return false;
}
TypeScript
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function deepEqual(o1: any, o2: any): boolean {
    if (o1 === o2) return true;
    if (typeof o1 !== typeof o2) return false;
    if (o1 === null || o2 === null) return o1 === o2;
    if (Array.isArray(o1) && Array.isArray(o2)) {
        if (o1.length !== o2.length) return false;
        for (let i = 0; i < o1.length; ++i) {
            if (!deepEqual(o1[i], o2[i])) return false;
        }
        return true;
    }
    if (typeof o1 === 'object' && typeof o2 === 'object') {
        const k1 = Object.keys(o1), k2 = Object.keys(o2);
        if (k1.length !== k2.length) return false;
        k1.sort(); k2.sort();
        for (let i = 0; i < k1.length; ++i) {
            if (k1[i] !== k2[i]) return false;
            if (!deepEqual(o1[k1[i]], o2[k2[i]])) return false;
        }
        return true;
    }
    return false;
}

Complexity

  • ⏰ Time complexity: O(N) where N = total number of nodes/values in the structure.
  • 🧺 Space complexity: O(H) where H = max nesting depth (recursion stack).