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Problem solution · TypeScript

Immutability Helper

Immutability Helper: a TypeScript solution using depth-first search. Learn the idea, check the complexity, and read the full code, with credit to walkccc LeetCode Solutions.

Technique
Depth-first search
Source
walkccc LeetCode Solutions
Length
115 lines
Start with the idea.

Try the problem first. If you get stuck, read the approach below, then write your own solution. The full code is at the bottom.

Approach

Depth-first search

For Immutability Helper, the implementation follows one branch at a time, making it suitable for components, trees, backtracking, or dependency exploration.

  1. Define the state carried into one recursive or stack frame.
  2. Mark or choose the current state before exploring children.
  3. Combine child results or undo the choice when the branch finishes.

Code notes

  • 115 lines of TypeScript from the credited upstream file 2691.ts.
  • The implementation visibly relies on sequence storage, ordered lookup.
  • 2 loop blocks detected.

Complexity

Count unique states for graph traversal; for backtracking, count the branching factor and maximum depth.

Check the problem constraints before deciding whether this complexity will pass.

Source

Code and credit

This code comes from walkccc LeetCode Solutions by P.-Y. Chen (walkccc) and is used under the MIT licence.

Open problem ↗Original source ↗
Full codeImmutability Helper · TypeScriptTypeScript
Use this to learn the idea, then write your own version.
type JSONValue =  | null  | boolean  | number  | string  | JSONValue[]  | { [key: string]: JSONValue };type InputObj = Record<string, JSONValue> | Array<JSONValue>; type RecursiveHandler = {  set: (target: any, prop: string, value: any) => boolean;  get: (target: any, prop: string) => unknown;}; const isObject = (o: any) => o !== null && typeof o === 'object'; // Access history of propertiesclass AccessHistory {  value: JSONValue | null = null;  props: Map<string, AccessHistory> = new Map();} class ImmutableHelper {  private obj: InputObj;   constructor(obj: InputObj) {    this.obj = obj;  }   produce(mutator: (obj: InputObj) => void): InputObj {    // Creates a proxied object to track property access history.    function createProxiedObj(      obj: InputObj,      accessHistory: AccessHistory    ): InputObj {      const handler: RecursiveHandler = {        // 'set' trap intercepts property assignment.        set(_, prop, value) {          if (!accessHistory.props.has(prop)) {            accessHistory.props.set(prop, new AccessHistory());          }          accessHistory.props.get(prop)!.value = value;          return true;        },        // 'get' trap intercepts property access.        get(_, prop) {          if (accessHistory.value !== null) {            return accessHistory.value;          }          if (!accessHistory.props.has(prop)) {            accessHistory.props.set(prop, new AccessHistory());          }          if (accessHistory.props.get(prop)!.value !== null) {            return accessHistory.props.get(prop)!.value;          }          if (isObject(obj[prop])) {            // Recursively create a proxed object for object property.            return createProxiedObj(              obj[prop] as InputObj,              accessHistory.props.get(prop)! as AccessHistory            );          }          return obj[prop];        },      };      return new Proxy(obj, handler);    }     // Returns true if there are mutated properties in the access history;    // otherwise, returns false and deletes the unnecessary properties.    function deleteUnmutatedProps(accessHistory: AccessHistory): boolean {      if (accessHistory.value !== null) {        return true;      }      let hasMutation = false;      for (const [prop, childAccessHistory] of [...accessHistory.props]) {        if (deleteUnmutatedProps(childAccessHistory)) {          hasMutation = true;        } else {          accessHistory.props.delete(prop);        }      }      return hasMutation;    }     // Function to transform the original object based on the access history    function transform(obj: InputObj, accessHistory: AccessHistory): InputObj {      if (accessHistory.value !== null) {        return accessHistory.value as InputObj;      }      if (accessHistory.props.size === 0) {        return obj;      }      if (!isObject(obj)) {        return obj;      }      let clone = Array.isArray(obj) ? [...obj] : { ...obj };      for (const [prop, childAccessHistory] of [...accessHistory.props]) {        clone[prop] = transform(obj[prop] as InputObj, childAccessHistory);      }      return clone;    }     const accessHistory = new AccessHistory();    const proxiedObj = createProxiedObj(this.obj, accessHistory);    // Apply the mutator function on the proxied object. This will also record    // the property access history in `accessHistory`.    mutator(proxiedObj);    // Simplify the access history.    deleteUnmutatedProps(accessHistory);    // Transform the original object based on the simplified access history.    return transform(this.obj, accessHistory);  }}

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