Merge pull request frank-lam#36 from LimitSY/master

frank-lam · web-flow · commit 36dd31257665 · 2019-05-08T15:56:21.000+08:00
二分查找以及二叉树遍历
diff --git a/notes/数据结构与算法.md b/notes/数据结构与算法.md
@@ -132,12 +132,158 @@ https://github.com/CarpenterLee/JCFInternals/blob/049c84bb65a3114ba4b8355d83c490
 
 #### 二分查找法
 
-#### 二叉树遍历
+在有序表中，通过不断的二分判断mid与目标是否一致，并缩小目标所在区间。
 
-### 4.. 二分搜索树
+**代码实现**
+
+```java
+// 非递归实现
+private static int search(int[] data, int l, int r, int target) {
+    int mid;
+    while(l < r) {
+        mid = (l + r) / 2;
+        if(data[mid] == target) {
+            return mid;
+        } else if(data[mid] < target) {
+            l = mid + 1;
+        } else {
+            r = mid;
+        }
+    }
+    return -1;
+}
+// 递归实现
+private static int searchDfs(int[] data, int l, int r, int target) {
+    if(l >= r) {
+        return -1;
+    }
+    int mid = (l + r) / 2;
+    if(target == data[mid]) {
+        return mid;
+    } else if(target > data[mid]) {
+        return searchDfs(data, mid + 1, r, target);
+    } else {
+        return searchDfs(data, l, mid, target);
+    }
+}
+```
+
+##### 
+
+### 4.. 二叉树遍历
 
 #### 深度优先遍历（前序、中序、后序遍历）
 
+```C++
+/**
+ * 前序遍历 非递归实现
+ * Definition for a binary tree node.
+ * struct TreeNode {
+ *     int val;
+ *     TreeNode *left;
+ *     TreeNode *right;
+ *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
+ * };
+ */
+class Solution {
+public:
+    vector<int> preorderTraversal(TreeNode* root) {
+        vector<int> ans;
+        TreeNode* node = root;
+        stack<TreeNode*> s;
+        map<TreeNode*, bool> M;
+        if(node != NULL) {
+            s.push(node);
+            while (!s.empty()) {
+                node = s.top();
+                if (!M[node]) {
+                    ans.push_back(node->val);
+                    M[node] = true;
+                }
+                if (node->left != NULL) {
+                    s.push(node->left);
+                    node->left = NULL;
+                } else if (node->right != NULL) {
+                    s.push(node->right);
+                    node->right = NULL;
+                } else {
+                    s.pop();
+                }
+            }
+        }
+        return ans;
+    }
+};
+```
+
+```c++
+/**
+ * 中序遍历
+ * Definition for a binary tree node.
+ * struct TreeNode {
+ *     int val;
+ *     TreeNode *left;
+ *     TreeNode *right;
+ *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
+ * };
+ */
+class Solution {
+public:
+    vector<int> inorderTraversal(TreeNode* root) {
+        vector<int> ans;
+        if(root != NULL) {
+            traversal(root, ans);
+        }
+        return ans;
+    }
+    
+    void traversal(TreeNode* node, vector<int> &ans) {
+        if(node->left != NULL) {
+            traversal(node->left, ans);
+        }
+        ans.push_back(node->val);
+        if(node->right != NULL) {
+            traversal(node->right, ans);
+        }
+    }
+};
+```
+
+
+
+```c++
+/**
+ * 后序遍历
+ * Definition for a binary tree node.
+ * struct TreeNode {
+ *     int val;
+ *     TreeNode *left;
+ *     TreeNode *right;
+ *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
+ * };
+ */
+class Solution {
+public:
+    vector<int> postorderTraversal(TreeNode* root) {
+        vector<int> ans;
+        if(root != NULL) {
+            traversal(root, ans);
+        }
+        return ans;
+    }
+
+    void traversal(TreeNode* node, vector<int> &ans) {
+        if(node->left != NULL) {
+            traversal(node->left, ans);
+        }
+        if(node->right != NULL) {
+            traversal(node->right, ans);
+        }
+        ans.push_back(node->val);
+    }
+};
+```
+
 #### 广度优先遍历（层序遍历）
 
 ### 5. AVL树
