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solution098.cpp
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60 lines (54 loc) · 950 Bytes
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/**
* Validate Binary Search Tree
*
* cpselvis([email protected])
* September 29th, 2016
*/
#include<iostream>
#include<stack>
using namespace std;
struct TreeNode {
int val;
TreeNode *left;
TreeNode *right;
TreeNode(int x) : val(x), left(NULL), right(NULL) {}
};
class Solution {
public:
bool isValidBST(TreeNode* root) {
stack<TreeNode *> st;
TreeNode *pnode = root;
TreeNode *pre;
while(!st.empty() || pnode != NULL)
{
if (pnode != NULL)
{
st.push(pnode);
pnode = pnode -> left;
}
else
{
pnode = st.top();
st.pop();
if (pre != NULL && pnode -> val <= pre -> val)
{
return false;
}
else
{
pre = pnode;
}
pnode = pnode -> right;
}
}
return true;
}
};
int main(int argc, char **argv)
{
TreeNode *root = new TreeNode(1);
root -> left = new TreeNode(2);
root -> right = new TreeNode(3);
Solution s;
cout << s.isValidBST(root) << endl;
}