611. Valid Triangle Number

class Solution {
    public int triangleNumber(int[] nums) {
		int count = 0;
		for (int i = 0; i < nums.length; i++) {
			for (int j = i+1; j < nums.length; j++) {
				for (int k = j+1; k  nums[k] &&
						nums[i] + nums[k] > nums[j]&&  
						nums[j] + nums[k] > nums[i]) {
						count++;
					}
				}
			}
		}
		return count;
	}
}

653. Two Sum IV – Input is a BST

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
  public boolean findTarget(TreeNode root, int k) {
		ArrayList data = new ArrayList();
		traverers(root, data);
		for (int i  = 0 ; i < data.size() ; i++)
			for (int j  = 0 ; j < data.size() && i!=j ; j++)
				if (data.get(i) + data.get(j) == k)
					return true;

		return false;
	}

	private void traverers(TreeNode root, ArrayList data) {
		if (root != null) {
			data.add(root.val);
			traverers(root.left, data);
			traverers(root.right, data);
		}
	}
}

590. N-ary Tree Postorder Traversal

/*
// Definition for a Node.
class Node {
    public int val;
    public List children;

    public Node() {}

    public Node(int _val,List _children) {
        val = _val;
        children = _children;
    }
};
*/
class Solution {
   	public List postorder(Node root) {
		List out = new ArrayList();
		postorder(root, out);
		return out;
	}

	private void postorder(Node root, List out) {
		if( null != root){
		for (int i = 0; i < root.children.size(); i++)
			postorder(root.children.get(i), out);
		out.add(root.val);
        }
	}
}