Merge pull request #199 from nmydt/patch-2

添加 二叉树中递归带着回溯 Java代码

Author: youngyangyang04

problems/二叉树中递归带着回溯.md

@@ -175,7 +175,85 @@ if (cur->right) {
 
 
 Java：
+  100. 相同的树:递归代码
+  ```java
+  class Solution {
+    public boolean compare(TreeNode tree1, TreeNode tree2) {
+       
+        if(tree1==null && tree2==null)return true;
+        if(tree1==null || tree2==null)return false;
+        if(tree1.val!=tree2.val)return false;
+        // 此时就是：左右节点都不为空，且数值相同的情况
+        // 此时才做递归，做下一层的判断
+        boolean compareLeft = compare(tree1.left, tree2.left);       // 左子树：左、 右子树：左
+        boolean compareRight = compare(tree1.right, tree2.right);    // 左子树：右、 右子树：右
+        boolean isSame = compareLeft && compareRight;                  // 左子树：中、 右子树：中（逻辑处理）
+        return isSame;
+
+    }
+    boolean isSameTree(TreeNode p, TreeNode q) {
+        return compare(p, q);
+    }
+}
+  ```
+  257. 二叉树的所有路径: 回溯代码
+  ```java
+  class Solution {
+    public void traversal(TreeNode cur, List<Integer> path, List<String> result) {
+        path.add(cur.val);
+        // 这才到了叶子节点
+        if (cur.left == null && cur.right == null) {
+            String sPath="";
+            for (int i = 0; i < path.size() - 1; i++) {
+                sPath += ""+path.get(i);
+                sPath += "->";
+            }
+            sPath += path.get(path.size() - 1);
+            result.add(sPath);
+            return;
+        }
+        if (cur.left!=null) {
+            traversal(cur.left, path, result);
+            path.remove(path.size()-1); // 回溯
+        }
+        if (cur.right!=null) {
+            traversal(cur.right, path, result);
+            path.remove(path.size()-1); // 回溯
+        }
+    }
+    
+    public List<String> binaryTreePaths(TreeNode root) {
+        List<String> result = new LinkedList<>();
+        List<Integer> path = new LinkedList<>();
+        if (root == null) return result;
+        traversal(root, path, result);
+        return result;
+    }
+}
+
+  ```
+  如下为精简之后的递归代码：(257. 二叉树的所有路径)
+  ```java
+  class Solution {
+    public void traversal(TreeNode cur, String path, List<String> result) {
+        path += cur.val; // 中
+        if (cur.left == null && cur.right == null) {
+            result.add(path);
+            return;
+        }
+        if (cur.left!=null) traversal(cur.left, path + "->", result); // 左  回溯就隐藏在这里
+        if (cur.right!=null) traversal(cur.right, path + "->", result); // 右 回溯就隐藏在这里
+    }
 
+    public List<String> binaryTreePaths(TreeNode root) {
+        List<String> result = new LinkedList<>();
+        String path = "";
+        if (root == null) return result;
+        traversal(root, path, result);
+        return result;
+    }
+}
+  ```
 
 Python：