Add, Search, Delete Node in BST.

Add Node, Search Node, Delete Node, 的基本操作，被问了两次了。写出来。

http://quiz.geeksforgeeks.org/binary-search-tree-set-1-search-and-insertion/

// add the node;public TreeNode addNode(TreeNode root, int val) {if(root == null){root = new TreeNode(val);return root;}if(root.val == val) {return root;} else if(root.val > val) {root.left = addNode(root.left, val);} else { // root.val < val;root.right = addNode(root.right, val);}return root;}// search the node;public TreeNode searchNode(TreeNode root, int val) {if(root == null || root.val == val) {return root;}if(val < root.val){return searchNode(root.left, val);} else {return searchNode(root.right, val);}}

http://quiz.geeksforgeeks.org/binary-search-tree-set-2-delete/

delete node分三类，如上，左右两边都有的，那么就找最右边的最小的，copy到root，然后delete那个node；

// delete node; public TreeNode deleteNode(TreeNode root, int val) {if(root == null) return root;if(val < root.val){root.left = deleteNode(root.left, val);} else if(val > root.val) {root.right = deleteNode(root.right, val);} else { // root.val == val, find the treenode that needs to be deleted;if(root.left == null) {return root.right;} else if(root.right == null) {return root.left;} else { // root has left & right node;root.val = findInorderNextNode(root.right);root.right = deleteNode(root.right, root.val);}}return root;}