235.236. Lowest Common Ancestor of a Binary (Search) Tree--Recent public ancestor

235. Lowest Common Ancestor of a Binary Search Tree

Given A binary search tree (BST), find the lowest common ancestor (LCA) of the Given nodes in the BST.

According to the definition of the LCA in Wikipedia: "The lowest common ancestor is defined between," nodes V and W as the L Owest node in T, have both V and W as descendants (where we allow a node to be a descendant of itself). "

        _______6______       /                  ___2__          ___8__   /      \        /         0      _4       7       9         /           3   5

For example, the lowest common ancestor (LCA) of nodes and are 2 8 6 . Another example is LCA of nodes 2 4 2 and are, since a node can be a descendant of itself according to the L CA definition.

Treenode* lowestcommonancestor (treenode* root, treenode* p, treenode*q) { while(root) {if(P->val > Root->val && q->val > root->val) {Root= root->Right ; Continue; }        if(P->val < Root->val && Q->val < root->val) {Root= root->Left ; Continue; }        returnRoot; }    returnNULL;}

236. Lowest Common Ancestor of a Binary Tree

Given a binary tree, find the lowest common ancestor (LCA) of the Given nodes in the tree.

According to the definition of the LCA in Wikipedia: "The lowest common ancestor is defined between," nodes V and W as the L Owest node in T, have both V and W as descendants (where we allow a node to be a descendant of itself). "

        _______3______       /                  ___5__          ___1__   /      \        /         6      _2       0       8         /           7   4

For example, the lowest common ancestor (LCA) of nodes and are 5 1 3 . Another example is LCA of nodes 5 4 5 and are, since a node can be a descendant of itself according to the L CA definition.

(1) Find two nodes at a time recursively

Treenode* LowestCommonAncestor02 (treenode* root, treenode* p, treenode*q) {//return if found or not found, return NULL if not found    if(Root==null | | root = = P | | root = = q)returnRoot; //find the LCA in left treeTreenode* left = LowestCommonAncestor02 (root->Left , p, q); //find the LCA in right treetreenode* right = LowestCommonAncestor02 (root->Right , p, q); //left==null means both ' P ' and ' Q ' is not found in the left tree.    if(Left==null)returnRight ; //right==null means both ' P ' and ' Q ' is not found on right tree.    if(Right==null)returnLeft ; //Left!=null && Right!=null, which means ' P ' & ' Q ' is seperated in left and right tree.    returnRoot;}

(2) record the root node to the node of the first sequence traversal path, return the last same node in the path

BOOLFindpath (treenode* root, treenode* p, vector<treenode*>&path) {    if(Root==null)return false; if(Root = =p) {path.push_back (P); return true;    } path.push_back (root); if(Findpath (Root->left, p, path))return true; if(Findpath (Root->right, p, path))return true;            Path.pop_back (); return false;}//Ordinary, find the path and comapre the path.Treenode* LowestCommonAncestor01 (treenode* root, treenode* p, treenode*q) {vector<TreeNode*>path1, path2; if(!findpath (Root, P, path1))returnNULL; if(!findpath (Root, Q, path2))returnNULL; intLen = Path1.size () < Path2.size ()?path1.size (): Path2.size (); TreeNode* result =Root;  for(intI=0; i<len; i++) {        if(Path1[i]! =Path2[i]) {            returnresult; } result=Path1[i]; }    returnresult;}

235.236. Lowest Common Ancestor of a Binary (Search) Tree--Recent public ancestor