Check if a Binary Tree contains duplicate subtrees of size 2 or more


Related: Google – Find Duplicated Subtrees
Check if a Binary Tree contains duplicate subtrees of size 2 or more - GeeksforGeeks
Given a Binary Tree, check whether the Binary tree contains a duplicate sub-tree of size 2 or more.
Note : Two same leaf nodes are not considered as subtree size of a leaf node is one.


An Efficient solution based on tree serialization and hashing. The idea is to serialize subtrees as strings and store the strings in hash table. Once we find a serialized tree (which is not a leaf) already existing in hash-table, we return true.

string dupSubUtil(Node *root)
{
    string s = "";
    // If current node is NULL, return marker
    if (root == NULL)
        return s + MARKER;
    // If left subtree has a duplicate subtree.
    string lStr = dupSubUtil(root->left);
    if (lStr.compare(s) == 0)
       return s;
    // Do same for right subtree
    string rStr = dupSubUtil(root->right);
    if (rStr.compare(s) == 0)
       return s;
    // Serialize current subtree
    s = s + root->key + lStr + rStr;
    // If current subtree already exists in hash
    // table. [Note that size of a serialized tree
    // with single node is 3 as it has two marker
    // nodes.
    if (s.length() > 3 &&
        subtrees.find(s) != subtrees.end())
       return "";
    subtrees.insert(s);
    return s;
}

    string str = dupSubUtil(root);
    (str.compare("") == 0) ? cout << " Yes ":
                             cout << " No " ;
A simple solution is that, we pick every node of tree and try to find is any sub-tree of given tree is present in tree which is identical with that sub-tree. Here we can use below post to find if a subtree is present anywhere else in tree.

https://gist.github.com/SahilKadam/fc9c87d7f71d1495ea90c07e2ca3dcf9

https://discuss.leetcode.com/topic/19/find-duplicate-subtrees

http://ayushcshah.github.io/algorithm/binarytree/2016/04/01/detect-duplicate-subtrees.html

A simple solution is that, we pick every node of tree and try to find is any sub-tree of given tree is present in tree which is identical with that sub-tree. Here we can use below post to find if a subtree is present anywhere else in tree.
Check if a binary tree is subtree of another binary tree
The idea is based on the fact that inorder and preorder/postorder uniquely identify a binary tree. Tree S is a subtree of T if both inorder and preorder traversals of S arew substrings of inorder and preorder traversals of T respectively.
Following are detailed steps.
1) Find inorder and preorder traversals of T, store them in two auxiliary arrays inT[] and preT[].
2) Find inorder and preorder traversals of S, store them in two auxiliary arrays inS[] and preS[].
3) If inS[] is a subarray of inT[] and preS[] is a subarray preT[], then S is a subtree of T. Else not.
The above algorithm doesn't work for cases where a tree is present
in another tree, but not as a subtree. Consider the following example.

        Tree1
          x 
        /    \
      a       b
     /        
    c         


        Tree2
          x 
        /    \
      a       b
     /         \
    c            d

Inorder and Preorder traversals of the big tree or Tree2 are.

Inorder and Preorder traversals of small tree or Tree1 are

The Tree2 is not a subtree of Tree1, but inS[] and preS[] are
subarrays of inT[] and preT[] respectively.
The above algorithm can be extended to handle such cases by adding a special character whenever we encounter NULL in inorder and preorder traversals. Thanks to Shivam Goel for suggesting this extension.
class Passing {
 
    int i;
    int m = 0;
    int n = 0;
}
 
class BinaryTree {
 
    static Node root;
    Passing p = new Passing();
 
    String strstr(String haystack, String needle) {
        if (haystack == null || needle == null) {
            return null;
        }
        int hLength = haystack.length();
        int nLength = needle.length();
        if (hLength < nLength) {
            return null;
        }
        if (nLength == 0) {
            return haystack;
        }
        for (int i = 0; i <= hLength - nLength; i++) {
            if (haystack.charAt(i) == needle.charAt(0)) {
                int j = 0;
                for (; j < nLength; j++) {
                    if (haystack.charAt(i + j) != needle.charAt(j)) {
                        break;
                    }
                }
                if (j == nLength) {
                    return haystack.substring(i);
                }
            }
        }
        return null;
    }
 
    // A utility function to store inorder traversal of tree rooted
    // with root in an array arr[]. Note that i is passed as reference
    void storeInorder(Node node, char arr[], Passing i) {
        if (node == null) {
            arr[i.i++] = '$';
            return;
        }
        storeInorder(node.left, arr, i);
        arr[i.i++] = node.data;
        storeInorder(node.right, arr, i);
    }
 
    // A utility function to store preorder traversal of tree rooted
    // with root in an array arr[]. Note that i is passed as reference
    void storePreOrder(Node node, char arr[], Passing i) {
        if (node == null) {
            arr[i.i++] = '$';
            return;
        }
        arr[i.i++] = node.data;
        storePreOrder(node.left, arr, i);
        storePreOrder(node.right, arr, i);
    }
 
    /* This function returns true if S is a subtree of T, otherwise false */
    boolean isSubtree(Node T, Node S) {
        /* base cases */
        if (S == null) {
            return true;
        }
        if (T == null) {
            return false;
        }
 
        // Store Inorder traversals of T and S in inT[0..m-1]
        // and inS[0..n-1] respectively
        char inT[] = new char[100];
        String op1 = String.valueOf(inT);
        char inS[] = new char[100];
        String op2 = String.valueOf(inS);
        storeInorder(T, inT, p);
        storeInorder(S, inS, p);
        inT[p.m] = '\0';
        inS[p.m] = '\0';
 
        // If inS[] is not a substring of preS[], return false
        if (strstr(op1, op2) != null) {
            return false;
        }
 
        // Store Preorder traversals of T and S in inT[0..m-1]
        // and inS[0..n-1] respectively
        p.m = 0;
        p.n = 0;
        char preT[] = new char[100];
        char preS[] = new char[100];
        String op3 = String.valueOf(preT);
        String op4 = String.valueOf(preS);
        storePreOrder(T, preT, p);
        storePreOrder(S, preS, p);
        preT[p.m] = '\0';
        preS[p.n] = '\0';
 
        // If inS[] is not a substring of preS[], return false
        // Else return true
        return (strstr(op3, op4) != null);
    }

Time Complexity: Time worst case complexity of above solution is O(mn) where m and n are number of nodes in given two trees.
    /* A utility function to check whether trees with roots as root1 and
       root2 are identical or not */
    boolean areIdentical(Node root1, Node root2)
    {
  
        /* base cases */
        if (root1 == null && root2 == null)
            return true;
  
        if (root1 == null || root2 == null)
            return false;
  
        /* Check if the data of both roots is same and data of left and right
           subtrees are also same */
        return (root1.data == root2.data
                && areIdentical(root1.left, root2.left)
                && areIdentical(root1.right, root2.right));
    }
  
    /* This function returns true if S is a subtree of T, otherwise false */
    boolean isSubtree(Node T, Node S)
    {
        /* base cases */
        if (S == null)
            return true;
  
        if (T == null)
            return false;
  
        /* Check the tree with root as current node */
        if (areIdentical(T, S))
            return true;
  
        /* If the tree with root as current node doesn't match then
           try left and right subtrees one by one */
        return isSubtree(T.left, S)
                || isSubtree(T.right, S);
    }


Read full article from Check if a Binary Tree contains duplicate subtrees of size 2 or more - GeeksforGeeks

Labels

LeetCode (1432) GeeksforGeeks (1122) LeetCode - Review (1067) Review (882) Algorithm (668) to-do (609) Classic Algorithm (270) Google Interview (237) Classic Interview (222) Dynamic Programming (220) DP (186) Bit Algorithms (145) POJ (141) Math (137) Tree (132) LeetCode - Phone (129) EPI (122) Cracking Coding Interview (119) DFS (115) Difficult Algorithm (115) Lintcode (115) Different Solutions (110) Smart Algorithm (104) Binary Search (96) BFS (91) HackerRank (90) Binary Tree (86) Hard (79) Two Pointers (78) Stack (76) Company-Facebook (75) BST (72) Graph Algorithm (72) Time Complexity (69) Greedy Algorithm (68) Interval (63) Company - Google (62) Geometry Algorithm (61) Interview Corner (61) LeetCode - Extended (61) Union-Find (60) Trie (58) Advanced Data Structure (56) List (56) Priority Queue (53) Codility (52) ComProGuide (50) LeetCode Hard (50) Matrix (50) Bisection (48) Segment Tree (48) Sliding Window (48) USACO (46) Space Optimization (45) Company-Airbnb (41) Greedy (41) Mathematical Algorithm (41) Tree - Post-Order (41) ACM-ICPC (40) Algorithm Interview (40) Data Structure Design (40) Graph (40) Backtracking (39) Data Structure (39) Jobdu (39) Random (39) Codeforces (38) Knapsack (38) LeetCode - DP (38) Recursive Algorithm (38) String Algorithm (38) TopCoder (38) Sort (37) Introduction to Algorithms (36) Pre-Sort (36) Beauty of Programming (35) Must Known (34) Binary Search Tree (33) Follow Up (33) prismoskills (33) Palindrome (32) Permutation (31) Array (30) Google Code Jam (30) HDU (30) Array O(N) (29) Logic Thinking (29) Monotonic Stack (29) Puzzles (29) Code - Detail (27) Company-Zenefits (27) Microsoft 100 - July (27) Queue (27) Binary Indexed Trees (26) TreeMap (26) to-do-must (26) 1point3acres (25) GeeksQuiz (25) Merge Sort (25) Reverse Thinking (25) hihocoder (25) Company - LinkedIn (24) Hash (24) High Frequency (24) Summary (24) Divide and Conquer (23) Proof (23) Game Theory (22) Topological Sort (22) Lintcode - Review (21) Tree - Modification (21) Algorithm Game (20) CareerCup (20) Company - Twitter (20) DFS + Review (20) DP - Relation (20) Brain Teaser (19) DP - Tree (19) Left and Right Array (19) O(N) (19) Sweep Line (19) UVA (19) DP - Bit Masking (18) LeetCode - Thinking (18) KMP (17) LeetCode - TODO (17) Probabilities (17) Simulation (17) String Search (17) Codercareer (16) Company-Uber (16) Iterator (16) Number (16) O(1) Space (16) Shortest Path (16) itint5 (16) DFS+Cache (15) Dijkstra (15) Euclidean GCD (15) Heap (15) LeetCode - Hard (15) Majority (15) Number Theory (15) Rolling Hash (15) Tree Traversal (15) Brute Force (14) Bucket Sort (14) DP - Knapsack (14) DP - Probability (14) Difficult (14) Fast Power Algorithm (14) Pattern (14) Prefix Sum (14) TreeSet (14) Algorithm Videos (13) Amazon Interview (13) Basic Algorithm (13) Codechef (13) Combination (13) Computational Geometry (13) DP - Digit (13) LCA (13) LeetCode - DFS (13) Linked List (13) Long Increasing Sequence(LIS) (13) Math-Divisible (13) Reservoir Sampling (13) mitbbs (13) Algorithm - How To (12) Company - Microsoft (12) DP - Interval (12) DP - Multiple Relation (12) DP - Relation Optimization (12) LeetCode - Classic (12) Level Order Traversal (12) Prime (12) Pruning (12) Reconstruct Tree (12) Thinking (12) X Sum (12) AOJ (11) Bit Mask (11) Company-Snapchat (11) DP - Space Optimization (11) Dequeue (11) Graph DFS (11) MinMax (11) Miscs (11) Princeton (11) Quick Sort (11) Stack - Tree (11) 尺取法 (11) 挑战程序设计竞赛 (11) Coin Change (10) DFS+Backtracking (10) Facebook Hacker Cup (10) Fast Slow Pointers (10) HackerRank Easy (10) Interval Tree (10) Limited Range (10) Matrix - Traverse (10) Monotone Queue (10) SPOJ (10) Starting Point (10) States (10) Stock (10) Theory (10) Tutorialhorizon (10) Kadane - Extended (9) Mathblog (9) Max-Min Flow (9) Maze (9) Median (9) O(32N) (9) Quick Select (9) Stack Overflow (9) System Design (9) Tree - Conversion (9) Use XOR (9) Book Notes (8) Company-Amazon (8) DFS+BFS (8) DP - States (8) Expression (8) Longest Common Subsequence(LCS) (8) One Pass (8) Quadtrees (8) Traversal Once (8) Trie - Suffix (8) 穷竭搜索 (8) Algorithm Problem List (7) All Sub (7) Catalan Number (7) Cycle (7) DP - Cases (7) Facebook Interview (7) Fibonacci Numbers (7) Flood fill (7) Game Nim (7) Graph BFS (7) HackerRank Difficult (7) Hackerearth (7) Inversion (7) Kadane’s Algorithm (7) Manacher (7) Morris Traversal (7) Multiple Data Structures (7) Normalized Key (7) O(XN) (7) Radix Sort (7) Recursion (7) Sampling (7) Suffix Array (7) Tech-Queries (7) Tree - Serialization (7) Tree DP (7) Trie - Bit (7) 蓝桥杯 (7) Algorithm - Brain Teaser (6) BFS - Priority Queue (6) BFS - Unusual (6) Classic Data Structure Impl (6) DP - 2D (6) DP - Monotone Queue (6) DP - Unusual (6) DP-Space Optimization (6) Dutch Flag (6) How To (6) Interviewstreet (6) Knapsack - MultiplePack (6) Local MinMax (6) MST (6) Minimum Spanning Tree (6) Number - Reach (6) Parentheses (6) Pre-Sum (6) Probability (6) Programming Pearls (6) Rabin-Karp (6) Reverse (6) Scan from right (6) Schedule (6) Stream (6) Subset Sum (6) TSP (6) Xpost (6) n00tc0d3r (6) reddit (6) AI (5) Abbreviation (5) Anagram (5) Art Of Programming-July (5) Assumption (5) Bellman Ford (5) Big Data (5) Code - Solid (5) Code Kata (5) Codility-lessons (5) Coding (5) Company - WMware (5) Convex Hull (5) Crazyforcode (5) DFS - Multiple (5) DFS+DP (5) DP - Multi-Dimension (5) DP-Multiple Relation (5) Eulerian Cycle (5) Graph - Unusual (5) Graph Cycle (5) Hash Strategy (5) Immutability (5) Java (5) LogN (5) Manhattan Distance (5) Matrix Chain Multiplication (5) N Queens (5) Pre-Sort: Index (5) Quick Partition (5) Quora (5) Randomized Algorithms (5) Resources (5) Robot (5) SPFA(Shortest Path Faster Algorithm) (5) Shuffle (5) Sieve of Eratosthenes (5) Strongly Connected Components (5) Subarray Sum (5) Sudoku (5) Suffix Tree (5) Swap (5) Threaded (5) Tree - Creation (5) Warshall Floyd (5) Word Search (5) jiuzhang (5)

Popular Posts