public class 剑指Offer_32_I_从上到下打印二叉树 {
public int[] levelOrder(TreeNode root) {
if (root == null) return new int[0];
Queue<TreeNode> queue = new LinkedList<>();
List<Integer> temp = new ArrayList<>();
queue.offer(root);
while (!queue.isEmpty()) {
TreeNode curNode = queue.poll();
temp.add(curNode.val);
if (curNode.left != null) queue.offer(curNode.left);
if (curNode.right != null) {
queue.offer(curNode.right);
}
}
int[] res = new int[temp.size()];
int curI = 0;
for (Integer integer : temp) {
res[curI++] = integer;
}
return res;
}
}
public class 剑指Offer_32_II_从上到下打印二叉树II {
public List<List<Integer>> levelOrder(TreeNode root) {
List<List<Integer>> res = new ArrayList<>();
if (root == null) return res;
Queue<TreeNode> queue = new LinkedList<>();
queue.offer(root);
while (!queue.isEmpty()) {
int size = queue.size();
List<Integer> temp = new ArrayList<>();
for (int i = 0; i < size; i++) {
TreeNode curNode = queue.poll();
temp.add(curNode.val);
if (curNode.left != null) queue.offer(curNode.left);
if (curNode.right != null) queue.offer(curNode.right);
}
res.add(temp);
}
return res;
}
}
public class 剑指Offer_32_III从上到下打印二叉树III {
public List<List<Integer>> levelOrder(TreeNode root) {
List<List<Integer>> res = new ArrayList<>();
if (root == null) return res;
Queue<TreeNode> queue = new LinkedList<>();
queue.offer(root);
boolean flag = false;
while (!queue.isEmpty()) {
int size = queue.size();
List<Integer> temp = new ArrayList<>();
for (int i = 0; i < size; i++) {
TreeNode curNode = queue.poll();
temp.add(curNode.val);
if (curNode.left != null) queue.offer(curNode.left);
if (curNode.right != null) queue.offer(curNode.right);
}
if (flag) Collections.reverse(temp);
flag = !flag;
res.add(temp);
}
return res;
}
}
public class 剑指Offer_33_二叉搜索树的后序遍历序列 {
public boolean verifyPostorder(int[] postorder) {
return process(postorder, 0, postorder.length - 1);
}
private boolean process(int[] postorder, int l, int r) {
if (l >= r) return true;
int p = l;
while (postorder[p] < postorder[r]) p++;
int m = p;
while (postorder[p] > postorder[r]) p++;
return p == r && process(postorder, l, m - 1) && process(postorder, m, r - 1);
}
}
public class 剑指Offer_34_二叉树中和为某一值的路径 {
private List<List<Integer>> list;
private List<Integer> res;
public List<List<Integer>> pathSum(TreeNode root, int sum) {
list = new ArrayList<>();
if (root == null) return list;
res = new ArrayList<>();
dfs(root, sum);
return list;
}
private void dfs(TreeNode root, int sum) {
if (root == null) {
if (sum == 0) {
list.add(new ArrayList<>(res));
}
return;
}
res.add(root.val);
if (root.left == null) {
dfs(root.right, sum - root.val);
} else if (root.right == null) {
dfs(root.left, sum - root.val);
} else {
dfs(root.left, sum - root.val);
dfs(root.right, sum - root.val);
}
res.remove(res.size() - 1);
}
}