42. 450. Delete Node in a BST

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Solution {
    public TreeNode deleteNode(TreeNode root, int key) {
        if(root==null){
            return root;
        }

        if(key<root.val){
            root.left = deleteNode(root.left,key);
        }else if(key>root.val){
            root.right = deleteNode(root.right,key);
        }else{
            if(root.left==null){
                return root.right;
            }else if(root.right==null){
                return root.left;
            }else{
                root.val = minValue(root.right);//right side min value
                root.right = deleteNode(root.right,root.val);
            }
        }
        return root;
        
    }

    private int minValue(TreeNode root){
        int minVal = root.val;
        while(root.left!=null){
            minVal = root.left.val;
            root = root.left;
        }
        return minVal;
    }
}