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2415:反转二叉树的奇数层

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轩辕龙儿 2022-09-20 22:58:12 +08:00
parent 77771cea9d
commit 4814e2056f
1 changed files with 59 additions and 37 deletions
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96
src/main/java/leetcode/editor/cn/ReverseOddLevelsOfBinaryTree.java
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@ -65,7 +65,7 @@ public class ReverseOddLevelsOfBinaryTree {
// 测试代码 // 测试代码
Solution solution = new ReverseOddLevelsOfBinaryTree().new Solution(); Solution solution = new ReverseOddLevelsOfBinaryTree().new Solution();
//TreeNode root = new TreeNode(Arrays.asList(2, 3, 5, 8, 13, 21, 34)); //TreeNode root = new TreeNode(Arrays.asList(2, 3, 5, 8, 13, 21, 34));
TreeNode root = new TreeNode(Arrays.asList(7,13,11)); TreeNode root = new TreeNode(Arrays.asList(7, 13, 11));
solution.reverseOddLevels(root); solution.reverseOddLevels(root);
} }
//leetcode submit region begin(Prohibit modification and deletion) //leetcode submit region begin(Prohibit modification and deletion)
@ -86,47 +86,69 @@ public class ReverseOddLevelsOfBinaryTree {
* } * }
*/ */
class Solution { class Solution {
// BFS
//public TreeNode reverseOddLevels(TreeNode root) {
// /*
// 如果是空节点直接返回
// */
// if (root == null) {
// return null;
// }
// // 队列存入每层的节点
// Queue<TreeNode> queue = new LinkedList<>();
// queue.add(root);
// int level = 0;
// while (!queue.isEmpty()) {
// /*
// 拿出每层的节点放入列表中，并将下一层的节点放入队列中
// */
// int size = queue.size();
// List<TreeNode> nodeList = new ArrayList<>();
// for (int i = 0; i < size; i++) {
// TreeNode node = queue.poll();
// nodeList.add(node);
// if (node.left != null) {
// queue.add(node.left);
// queue.add(node.right);
// }
// }
// /*
// 奇数层，在列表中交换收尾节点的值
// */
// if (level == 1) {
// int nodeSize = nodeList.size();
// for (int i = 0; i < nodeSize / 2; i++) {
// int num = nodeList.get(i).val;
// nodeList.get(i).val = nodeList.get(nodeSize - i - 1).val;
// nodeList.get(nodeSize - i - 1).val = num;
// }
// }
// // 改变奇偶层
// level = 1 - level;
// }
// return root;
//}
// DFS
public TreeNode reverseOddLevels(TreeNode root) { public TreeNode reverseOddLevels(TreeNode root) {
/*
如果是空节点直接返回
*/
if (root == null) { if (root == null) {
return null; return root;
}
// 队列存入每层的节点
Queue<TreeNode> queue = new LinkedList<>();
queue.add(root);
int level = 0;
while (!queue.isEmpty()) {
/*
拿出每层的节点放入列表中，并将下一层的节点放入队列中
*/
int size = queue.size();
List<TreeNode> nodeList = new ArrayList<>();
for (int i = 0; i < size; i++) {
TreeNode node = queue.poll();
nodeList.add(node);
if (node.left != null) {
queue.add(node.left);
queue.add(node.right);
}
}
/*
奇数层，在列表中交换收尾节点的值
*/
if (level == 1) {
int nodeSize = nodeList.size();
for (int i = 0; i < nodeSize / 2; i++) {
int num = nodeList.get(i).val;
nodeList.get(i).val = nodeList.get(nodeSize - i - 1).val;
nodeList.get(nodeSize - i - 1).val = num;
}
}
// 改变奇偶层
level = 1 - level;
} }
dfs(root.left, root.right, 1);
return root; return root;
} }
private void dfs(TreeNode left, TreeNode right, int level) {
if (left == null) {
return;
}
if (level == 1) {
int tmp = left.val;
left.val = right.val;
right.val = tmp;
}
dfs(left.left, right.right, 1 - level);
dfs(left.right, right.left, 1 - level);
}
} }
//leetcode submit region end(Prohibit modification and deletion) //leetcode submit region end(Prohibit modification and deletion)