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Copy pathRecoverBST.cpp
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47 lines (44 loc) · 1.16 KB
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/**
Two elements of a binary search tree (BST) are swapped by mistake.
Recover the tree without changing its structure.
Note:
A solution using O(n) space is pretty straight forward.
Could you devise a constant space solution?
*/
/**
* Definition for binary tree
* struct TreeNode {
* int val;
* TreeNode *left;
* TreeNode *right;
* TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
class Solution {
public:
void recoverTreeHelper(TreeNode *root, TreeNode* &pre, TreeNode* &fst, TreeNode* &snd){
if(!root) return;
recoverTreeHelper(root->left, pre, fst, snd);
if(pre!=NULL && pre->val>root->val){
if(fst==NULL){
fst=pre;
snd=root;
}
else
snd=root;
}
pre=root;
recoverTreeHelper(root->right, pre, fst, snd);
}
void recoverTree(TreeNode *root) {
TreeNode *fst=NULL;
TreeNode *snd=NULL;
TreeNode *pre=NULL;
recoverTreeHelper(root, pre, fst, snd);
if(fst==NULL)
return;
int tmp = fst->val;
fst->val = snd->val;
snd->val = tmp;
}
};