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algorithm/Week_02/id_118/leetcode_236_118.java at master · algorithm001/algorithm · GitHub
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Week_02
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id_118
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leetcode_236_118.java
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algorithm
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Week_02
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id_118
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leetcode_236_118.java
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/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
// https://leetcode-cn.com/problems/lowest-common-ancestor-of-a-binary-tree/submissions/
// 236.二叉树的最近公共祖先
class
Solution
{
public
TreeNode
lowestCommonAncestor
(
TreeNode
root
,
TreeNode
p
,
TreeNode
q
) {
// root有任何一个是根节点，则它本身就是最近公共祖先
if
(
p
==
root
||
q
==
root
){
return
root
;
}
// 判断：p和q在不在左子树上
boolean
pLeft
=
find
(
root
.
left
,
p
);
boolean
qLeft
=
find
(
root
.
left
,
q
);
if
(
pLeft
&&
qLeft
){
// 都在左子树
return
lowestCommonAncestor
(
root
.
left
,
p
,
q
);
}
else
if
(!
pLeft
&& !
qLeft
){
// 都在右子树
return
lowestCommonAncestor
(
root
.
right
,
p
,
q
);
}
else
{
// 一个在左子树，一个在右子树，则当前节点就是最近公共祖先。
return
root
;
}
}
// 检查 root这棵树中，是否有节点x
boolean
find
(
TreeNode
root
,
TreeNode
x
){
if
(
root
==
null
){
return
false
;
}
if
(
root
==
x
){
return
true
;
}
if
(
root
.
left
==
null
&&
root
.
right
==
null
){
return
false
;
}
else
if
(
root
.
left
==
null
&&
root
.
right
!=
null
){
return
find
(
root
.
right
,
x
);
}
else
if
(
root
.
left
!=
null
&&
root
.
right
==
null
){
return
find
(
root
.
left
,
x
);
}
else
{
return
find
(
root
.
left
,
x
) ||
find
(
root
.
right
,
x
);
}
}
}
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