236. Lowest Common Ancestor of a Binary Tree
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236. Lowest Common Ancestor of a Binary Tree
Given a binary tree, find the lowest common ancestor (LCA) of two given nodes in the tree.
According to the definition of LCA on Wikipedia: “The lowest common ancestor is defined between two nodes v and w as the lowest node in T that has 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 5
and 1
is 3
. Another example is LCA of nodes 5
and 4
is 5
, since a node can be a descendant of itself according to the LCA definition.
/** * Definition for a binary tree node. * struct TreeNode { * int val; * TreeNode *left; * TreeNode *right; * TreeNode(int x) : val(x), left(NULL), right(NULL) {} * }; */class Solution { bool hasnode(TreeNode* root,TreeNode* p) { if(!root) return false; if(root==p) return true; return hasnode(root->left,p)||hasnode(root->right,p); }public: TreeNode* lowestCommonAncestor(TreeNode* root, TreeNode* p, TreeNode* q) { if(!root) return NULL; if(root==p||root==q) return root; if((hasnode(root->left,p)&&hasnode(root->right,q))||(hasnode(root->left,q)&&hasnode(root->right,p))) return root; TreeNode* r=lowestCommonAncestor(root->left,p,q); return r==NULL?lowestCommonAncestor(root->right,p,q):r; }};
转载于点击打开链接
TreeNode* lowestCommonAncestor(TreeNode* root, TreeNode* p, TreeNode* q) { if(!root||root==p||root==q) return root; TreeNode* left=lowestCommonAncestor(root->left,p,q); TreeNode* right=lowestCommonAncestor(root->right,p,q); // if(left&&right) return root; //if(left) return left; //else return right;以上等价于下面的return语句 return !left?right:!right?left:root; }
如果当前节点包含p,而它同一层的另一子树包含q,返回两者的父节点。否则,只在某一子树下接着遍历。
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- Lowest Common Ancestor of a Binary Tree
- Lowest Common Ancestor of a Binary Tree
- Lowest Common Ancestor of a Binary Tree
- Lowest Common Ancestor of a Binary Tree
- Lowest Common Ancestor of a Binary Tree
- Lowest Common Ancestor of a Binary Tree
- Lowest Common Ancestor of a Binary Tree
- Lowest Common Ancestor of a Binary Tree
- Lowest Common Ancestor of a Binary Tree
- Lowest Common Ancestor of a Binary Tree(***)
- Lowest Common Ancestor of a Binary Tree
- Lowest Common Ancestor of a Binary Tree
- Lowest Common Ancestor of a Binary Tree
- Lowest Common Ancestor of a Binary Tree
- Lowest Common Ancestor of a Binary Tree
- Lowest Common Ancestor of a Binary Tree
- Lowest Common Ancestor of a Binary Tree
- Lowest Common Ancestor of a Binary Tree
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