270. Closest Binary Search Tree Value

    
    /*
     * 270. Closest Binary Search Tree Value
     * 2016-6-25 by Mingyang
     */
      public int closestValue(TreeNode root, double target) {
            int closest = root.val;  
            double min = Double.MAX_VALUE;  
            while(root!=null) {  
                if( Math.abs(root.val - target) < min  ) {  
                    min = Math.abs(root.val - target);  
                    closest = root.val;  
                }                
                if(target < root.val) {  
                    root = root.left;  
                } else if(target > root.val) {  
                    root = root.right;  
                } else {  
                    return root.val;  
                }  
            }            
            return closest;  
        }

    //下面就是recursive的方法，思路很清晰，就是root和左子树或者右子树进行比较大小
    public int closestValue1(TreeNode root, double target) {
        int a = root.val;
        TreeNode kid = target < a ? root.left : root.right;
        if (kid == null)
            return a;
        int b = closestValue1(kid, target);
        return Math.abs(a - target) < Math.abs(b - target) ? a : b;
    }