二叉树遍历code

src/ds/tree/TreeTraverse.java

@@ -0,0 +1,111 @@
+package ds.tree;
+
+import ds.linklist.Node;
+import leecode.tree.TreeNode;
+
+import java.util.Stack;
+
+/**
+ * @author Wen
+ * @date 2022/9/1 22:03
+ */
+public class TreeTraverse {
+
+    //前序
+    public void pre(TreeNode h) {
+        if (h == null) {
+            return;
+        }
+        Stack<TreeNode> stack = new Stack<>();
+        stack.push(h);
+        while (!stack.isEmpty()) {
+            TreeNode pop = stack.pop();
+            System.out.println(pop.val);
+            if (pop.right != null) {
+                stack.push(pop.right);
+            }
+            if (pop.left != null) {
+                stack.push(pop.left);
+            }
+        }
+    }
+
+    //中序
+    public void in(TreeNode h) {
+        if (h == null) {
+            return;
+        }
+        Stack<TreeNode> stack = new Stack<>();
+        while (!stack.isEmpty() || h != null) {
+            if (h != null) {
+                stack.push(h);
+                h = h.left;
+            } else {
+                h = stack.pop();
+                System.out.println(h.val);
+                h = h.right;
+            }
+        }
+    }
+
+    //后序
+    public void pos(TreeNode h) {
+        if (h == null) {
+            return;
+        }
+        Stack<TreeNode> stack = new Stack<>();
+        Stack<TreeNode> stack2 = new Stack<>();
+        stack.push(h);
+        while (!stack.isEmpty()) {
+            TreeNode pop = stack.pop();
+            stack2.push(pop);
+            if (pop.left != null) {
+                stack.push(pop.left);
+            }
+            if (pop.right != null) {
+                stack.push(pop.right);
+            }
+        }
+        while (!stack2.isEmpty()) {
+            System.out.println(stack2.pop().val);
+        }
+    }
+
+    /**
+     * c标记树的处理路径，先处理左树。
+     * 没有左树时开始弹出，弹出后h移动到c的位置记录上一次的弹出位置
+     * c指向下一个将要弹出的节点，这时候将判断h与c的位置关系，
+     * h如果既不是c的左子树也不是右子树，按后序遍历的顺序来看相当于c还未处理左右子树，此时优先处理左子树，然后处理右子树
+     */
+    public void posPro(TreeNode h) {
+        if (h == null){
+            return;
+        }
+        TreeNode c;
+        Stack<TreeNode> stack = new Stack<>();
+        stack.push(h);
+        while (!stack.isEmpty()) {
+            //指向将要弹出的节点，但不弹出
+            c = stack.peek();
+            if (c.left != null && h != c.left && h != c.right) {
+                //c还没处理左子树
+                stack.push(c.left);
+                c = c.left;
+            } else if (c.right != null && h != c.right) {
+                //c还没处理右子树
+                stack.push(c.right);
+                c = c.right;
+            } else {
+                //c可以弹出了
+                c = stack.pop();
+                System.out.println(c.val);
+                h = c;
+            }
+        }
+    }
+
+    public static void main(String[] args) {
+        TreeTraverse treeTraverse = new TreeTraverse();
+        treeTraverse.posPro(TreeNode.parseTree(new Integer[]{1,2,3,4,5,6,7}));
+    }
+}