LeetCode(算法)- 236. 二叉树的最近公共祖先
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AC 代码
- Java
/**
* Definition for a binary tree node.
* public class TreeNode
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) val = x;
*
*/
// 解决方案(1)
class Solution
Queue<TreeNode> pQue = new LinkedList<>(), qQue = new LinkedList<>();
Map<TreeNode, Integer> pMap = new HashMap<>(), qMap = new HashMap<>();
public TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q)
dfs(root, p.val, pQue, pMap, 0);
dfs(root, q.val, qQue, qMap, 0);
TreeNode res = common();
return res;
TreeNode common()
TreeNode res;
while (!pQue.isEmpty() && !qQue.isEmpty())
TreeNode pe = pQue.peek();
TreeNode qe = qQue.peek();
if (pe.val == qe.val)
res = pQue.peek();
pQue.poll();
qQue.poll();
return res;
if (pMap.get(pe) > qMap.get(qe))
pQue.poll();
else if (pMap.get(pe) < qMap.get(qe))
qQue.poll();
else
pQue.poll();
qQue.poll();
return null;
boolean dfs(TreeNode node, int val, Queue<TreeNode> queue, Map<TreeNode, Integer> map, int l)
if (node == null)
return false;
if (node.val == val)
queue.offer(node);
map.put(node, l);
return true;
boolean left = dfs(node.left, val, queue, map, l + 1);
if (left)
queue.offer(node);
map.put(node, l);
return true;
boolean right = dfs(node.right, val, queue, map, l + 1);
if (right)
queue.offer(node);
map.put(node, l);
return true;
return false;
// 解决方案(2)
class Solution
public TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q)
if(root == null || root == p || root == q) return root;
TreeNode left = lowestCommonAncestor(root.left, p, q);
TreeNode right = lowestCommonAncestor(root.right, p, q);
if(left == null) return right;
if(right == null) return left;
return root;
- C++
/**
* 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
public:
TreeNode* lowestCommonAncestor(TreeNode* root, TreeNode* p, TreeNode* q)
if(root == nullptr || root == p || root == q) return root;
TreeNode *left = lowestCommonAncestor(root->left, p, q);
TreeNode *right = lowestCommonAncestor(root->right, p, q);
if(left == nullptr) return right;
if(right == nullptr) return left;
return root;
;
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