Asked in: NAMMA_YATRI
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Solution
#include <bits/stdc++.h>
using namespace std;
struct Node {
// ... rest of solution available after purchaseExplanation
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To solve this problem, the first step is to clearly understand the representation of the directory structure and the operations requested. The directory structure is modeled as a tree where each node corresponds to a directory, and each node can have multiple child directories with unique names. The root directory is given, and its children and further descendants are defined in the input. The main challenge is to implement efficient tree operations and maintain the tree structure as modifications (cut-paste and copy-paste) happen.
Step 1: Building the Directory Tree
You must parse the input lines to build the directory tree. Each line gives a directory and its immediate children. Since directory names are unique within their siblings, this will help you maintain a clear parent-child relationship.
Represent each directory as a node object with attributes:
- name (string)
- parent (pointer/reference to parent node)
- children (map/dictionary from child-name to child node)
Using a dictionary keyed by full path or by node references helps quick access during queries and commands.
Step 2: Understanding Paths
Commands and queries use paths such as "root/a/d". You need a method to quickly resolve any given path to its corresponding node in the tree. For this:
- Split the path by '/'
- Start from the root node and traverse children by name according to the path segments
- If any segment is missing or does not exist in the current node’s children, return an invalid path
Step 3: Implementing countDescendants(path)
This function must count all descendants of the directory at the given path. Descendants include children, grandchildren, and so on recursively.
- Locate the node corresponding to the path
- Perform a depth-first search (DFS) or breadth-first search (BFS) starting from that node to count all reachable nodes except the node itself
- Return the count or print "Invalid command" if the path does not exist
This step involves traversal of subtrees and must be efficient. To optimize, you could store the size of subtree at each node and update it dynamically during cut-paste and copy-paste operations to avoid recomputing the counts each time.
Step 4: Implementing cutPaste(src, dest)
This command moves the source directory and its entire subtree from its current parent to the destination directory. Key points to handle:
- Validate both src and dest paths exist
- Check that src is not an ancestor of dest (to avoid cycles and invalid moves)
- Ensure src is not equal to dest (no self-move)
- Check dest does not already have a child directory with the same name as src
- If valid, detach src from its current parent by removing it from the parent's children map
- Attach src as a child of dest by adding to dest’s children map
- Update parent pointers accordingly
- Update subtree sizes or cached counts to reflect the new structure
- Verify that the total number of nodes does not exceed 10^6 after operation; if it does, print "Invalid command"
If any validation fails, print "Invalid command" else print "OK".
Step 5: Implementing copyPaste(src, dest)
This operation copies the entire src subtree and attaches the copy under dest. Differences from cut-paste:
- The original src subtree remains unchanged
- A deep copy of the src subtree is created, duplicating all nodes and their children recursively
- Validate paths and constraints similar to cutPaste (no ancestor-descendant violation, no same-name child in dest)
- After deep copying, attach the copy to dest’s children and update parent pointers
- Update total nodes count and verify it doesn’t exceed limits
- Print "OK" if successful, else "Invalid command"
Step 6: Validation Rules
The constraints require careful checks before any operation:
- Paths must exist for source and destination
- No cycles or ancestor-descendant violations (src cannot be ancestor of dest)
- Source and destination cannot be the same
- Destination cannot have a child with the same name as source
- Node count limit (10^6) must be enforced after any modification
Implement helper functions to verify these conditions before performing cut or copy operations.
Step 7: Performance Considerations
- Since n and q can be up to 10^5 and total nodes can reach 10^6, solutions must be efficient in path lookup, subtree counting, and structural updates.
- Use hash maps/dictionaries for children to allow O(1) child lookup.
- Cache subtree sizes and maintain them incrementally to avoid expensive recalculations.
- For ancestor-descendant checks, techniques such as Euler tours with entry-exit timestamps or maintaining parent pointers with depth information can help quickly determine ancestry relations.
- Deep copying large subtrees in copyPaste must be done carefully, ideally recursively, but with attention to memory and performance.
Step 8: Edge Cases and Errors
- Commands referencing non-existent paths
- Moving root or trying to copy/move root
- Trying to move a directory into one of its descendants
- Duplicate child names on paste
- Large trees and very deep nested directories
- Commands that would cause total node count to exceed allowed limits
Summary:
- Construct a tree representation from input
- Efficiently resolve paths to nodes
- Implement countDescendants using cached subtree sizes or DFS
- Implement cutPaste and copyPaste with validations and structural updates
- Maintain data structures for fast lookups and updates
- Carefully handle all invalid scenarios and print correct outputs
Following this methodical approach ensures correctness, efficiency, and adherence to constraints for this complex directory tree manipulation problem.
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