find min num tree path

给个Tree 不一定是平衡的， 要求 把所有路径排序后 按字符串那样的比较大小方法 找出最小的路径 时间要求线性的。 比如 

    5 

    /  \ 

 10  3

 / \    /

1 7 8

路径有 5 10 1 ； 5 10 7 ； 5 3 8排序后 1 5 10 ； 5 7 10 ； 3 5 8；所以按字符串类型排序 为 1 5 10 < 3 5 8 < 5 7 10

public static void main(String[] args) {
		TreeNode t5 = new TreeNode(5);
		TreeNode t10 = new TreeNode(10);
		TreeNode t3 = new TreeNode(3);
		TreeNode t1 = new TreeNode(1);
		TreeNode t7 = new TreeNode(7);
		TreeNode t2 = new TreeNode(2);
		t5.left = t10;
		t5.right = t3;
		t10.left = t1;
		t10.right = t7;
		t3.left = t2;
		FindMinNumTreePath findMinTreePath = new FindMinNumTreePath();
		Result res = findMinTreePath.findMinimumNumber(t5);
		for (int i: res.list) {
			System.out.println(i);
		}
		System.out.println("min:" +res.min);
	}
	
	public Result findMinimumNumber(TreeNode root) {
		if (root == null) {
			return new Result();
		}
		if (root.left == null && root.right == null) {
			Result r = new Result();
			r.min = root.val;
			r.list.add(root.val);
			return r;
		}
		Result left = findMinimumNumber(root.left);
		Result right = findMinimumNumber(root.right);
		Result r = new Result();
		r.list.add(root.val);
		if (left.min < right.min) {
			r.list.addAll(left.list);
		} else {
			r.list.addAll(right.list);
		}
		r.min = Math.min(root.val, Math.min(left.min, right.min));
		return r;
	}

	class Result {
		int min;
		ArrayList<Integer> list;

		public Result() {
			min = Integer.MAX_VALUE;
			list = new ArrayList<Integer>();
		}
	}