Largest Subtree Which is a Binary Search Tree (BST)

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找到一个树中最大的BST subtree，题目来源：

http://leetcode.com/2010/11/largest-binary-search-tree-bst-in.html

算法： buttom-up, O(n)。

#include <iostream>#include <climits>using namespace std;struct TreeNode{int val;TreeNode *left;TreeNode *right;TreeNode(int v): val(v){}};int findLargestBSTSubstree(TreeNode *p, int &min, int &max, int &maxNodes, TreeNode *&largest){if(p == NULL) return 0;int minLeft = INT_MAX, maxLeft = INT_MIN, minRight = INT_MAX, maxRight = INT_MIN;int countLeft, countRight;countLeft = findLargestBSTSubstree(p->left, minLeft, maxLeft, maxNodes, largest);countRight = findLargestBSTSubstree(p->right, minRight, maxRight, maxNodes, largest);if(countLeft != -1 && countRight != -1 && maxLeft < p->val && p->val < minRight){int count = countLeft+countRight+1;if(count > maxNodes){maxNodes = count;largest = p;}if(countLeft == 0)min = p->val;elsemin = minLeft;if(countRight == 0)max = p->val;elsemax = maxRight;return count;}else{return -1;}}int main(){TreeNode *root = new TreeNode(10);root->left = new TreeNode(5);root->right = new TreeNode(15);root->left->left = new TreeNode(1);root->left->right = new TreeNode(8);root->right->right = new TreeNode(7);int min, max, maxNodes;TreeNode *largest;findLargestBSTSubstree(root, min, max, maxNodes, largest);cout << maxNodes << endl;cout << largest->val << endl;return 0;}

相关题目：http://leetcode.com/2010/11/largest-binary-search-tree-bst-in_22.html

Largest Binary Search Tree (BST) in a Binary Tree

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