Thursday, April 17, 2008

Check if a binary tree is a binary search tree

int isBST(struct node* node) {

if (node==NULL) return(true);
// false if the min of the left is > than us
if (node->left!=NULL && minValue(node->left) > node->data)
// false if the max of the right is <= than us
if (node->right!=NULL && maxValue(node->right) <= node->data)
// false if, recursively, the left or right is not a BST
if (!isBST(node->left) || !isBST(node->right))
// passing all that, it's a BST

int isBST2(struct node* node) {
return(isBSTUtil(node, INT_MIN, INT_MAX));
Returns true if the given tree is a BST and its
values are >= min and <= max.
int isBSTUtil(struct node* node, int min, int max) {
if (node==NULL) return(true);
// false if this node violates the min/max constraint
if (node->datadata>max) return(false);
// otherwise check the subtrees recursively,
// tightening the min or max constraint
isBSTUtil(node->left, min, node->data) &&
isBSTUtil(node->right, node->data+1, max)

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