Find kth number in a BST

递归实现，按照左根右的顺序来实现

1 #include 
     
       2 using namespace std; 3  4 struct Node 5 { 6     Node *left; 7     Node *right; 8     int val; 9     Node():left(NULL), right(NULL){}10 };11 12 Node *findKthElement(Node *node, int &K)13 {14     if (node == NULL)15         return NULL;16 17     Node *left = findKthElement(node->left, K);18 19     if (left != NULL)20         return left;21 22     K--;23 24     if (K == 0)25         return node;26 27     Node *right = findKthElement(node->right, K);28 29     return right;30 }31 32 int main()33 {34     Node node[10];35 36     for(int i = 0; i < 10; i++)37         node[i].val = i;38 39     node[4].left = &node[2];40     node[4].right = &node[7];41 42     node[2].left = &node[1];43     node[2].right = &node[3];44 45     node[1].left = &node[0];46 47     node[7].left = &node[6];48     node[7].right = &node[8];49 50     node[6].left = &node[5];51 52     node[8].right = &node[9];53 54     for(int i = 1; i <= 10; i++)55     {56         int k = i;57         Node *ret = findKthElement(&node[4], k);58         cout << i << "th element:" << ret->val << endl;59     }60 }