Dado un árbol binario, devuelve el orden de nivel ascendente transversal de los valores de sus nodos.
Por ejemplo, dado el árbol binario {3,9,20, #, #, 15,7},
3
/
9 20
/
15 7
devuelve su recorrido de orden de nivel como [[15,7], [9,20],[3]]
Solución Java
public List<ArrayList<Integer>> levelOrderBottom(TreeNode root) { ArrayList<ArrayList<Integer>> result = new ArrayList<ArrayList<Integer>>(); if(root == null){ return result; } LinkedList<TreeNode> current = new LinkedList<TreeNode>(); LinkedList<TreeNode> next = new LinkedList<TreeNode>(); current.offer(root); ArrayList<Integer> numberList = new ArrayList<Integer>(); // need to track when each level starts while(!current.isEmpty()){ TreeNode head = current.poll(); numberList.add(head.val); if(head.left != null){ next.offer(head.left); } if(head.right!= null){ next.offer(head.right); } if(current.isEmpty()){ current = next; next = new LinkedList<TreeNode>(); result.add(numberList); numberList = new ArrayList<Integer>(); } } //return Collections.reverse(result); ArrayList<ArrayList<Integer>> reversedResult = new ArrayList<ArrayList<Integer>>(); for(int i=result.size()-1; i>=0; i--){ reversedResult.add(result.get(i)); } return reversedResult; } |
