JSON Diff — Find Differences

Difficulty: Hard · Topics: JSON, Recursion, Tree Comparison · Acceptance: 100.0% of 4 submissions

Difficulty: Hard | Tags: JSON, Recursion, Tree Comparison

Description

Given two JSON objects (as strings or maps), find all differences between them. Return a structured diff that identifies:

Added keys (present in json2 but not json1)
Removed keys (present in json1 but not json2)
Modified values (key exists in both but values differ)

Support nested objects and arrays.

Implement:

jsonDiff(json1, json2) → List<Difference>

Where each Difference contains: path, type (ADDED/REMOVED/MODIFIED), oldValue, newValue.

Examples

Example 1:

Input:
  json1 = {"name": "Alice", "age": 30}
  json2 = {"name": "Alice", "age": 31, "city": "NYC"}

Output:
  [
    {path: "$.age",  type: MODIFIED, old: 30,    new: 31},
    {path: "$.city", type: ADDED,    old: null,  new: "NYC"}
  ]

Example 2 — Nested:

Input:
  json1 = {"user": {"name": "Alice", "address": {"city": "LA"}}}
  json2 = {"user": {"name": "Bob",   "address": {"city": "LA", "zip": "90001"}}}

Output:
  [
    {path: "$.user.name",        type: MODIFIED, old: "Alice", new: "Bob"},
    {path: "$.user.address.zip", type: ADDED,    old: null,    new: "90001"}
  ]

Example 3 — Array change:

Input:
  json1 = {"tags": ["java", "python"]}
  json2 = {"tags": ["java", "go"]}

Output:
  [
    {path: "$.tags[1]", type: MODIFIED, old: "python", new: "go"}
  ]

Constraints

JSON nesting depth ≤ 15.
Array comparison is index-based (not content-aware).
Both inputs must be valid JSON objects.
Key order does not matter.

Hints

Hint 1

Use recursion: at each level, compute the union of keys and compare.

Hint 2

Track the current path as you recurse (e.g., "$.user.address").

Follow-up

Support content-aware array diffing (detect insertions/deletions in arrays, not just index mismatch).

Practice this problem

Solve JSON Diff — Find Differences in the browser