Add Solution 105[CPP]

Author: KongJHong

solution/105.Construct Binary Tree from Preorder and Inorder Traversal/README.md

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+## 从前序与中序遍历序列构造二叉树
+
+### 问题描述
+根据一棵树的前序遍历与中序遍历构造二叉树。
+
+注意:
+你可以假设树中没有重复的元素。
+
+例如，给出
+```
+前序遍历 preorder = [3,9,20,15,7]
+中序遍历 inorder = [9,3,15,20,7]
+```
+
+返回如下的二叉树：
+```
+    3
+   / \
+  9  20
+    /  \
+   15   7
+```
+---------------
+
+### 思路
+
+利用树的前序遍历和中序遍历特性+递归实现
+
+对树进行前序遍历，每一个元素，在树的中序遍历中找到概元素；在中序遍历中，该元素的左边是它的左子树的全部元素，右边是它的右子树的全部元素，以此为递归条件，确定左右子树的范围
+
+```CPP
+/**
+ * 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:
+    TreeNode* buildTree(vector<int>& preorder, vector<int>& inorder) {
+        int pRight = preorder.size()-1;
+        int iRight = inorder.size()-1;
+        return build(preorder,inorder,0,pRight,0,iRight);
+    }
+    
+    
+    TreeNode* build(vector<int>& preorder,vector<int>& inorder,int pLeft,int pRight,int iLeft,int iRight){
+        if(pLeft > pRight)return NULL;
+        
+        TreeNode *node = new TreeNode(preorder[pLeft]);
+        int idx = iLeft;
+        
+        while(inorder[idx] != preorder[pLeft])idx++;
+        node->left = build(preorder,inorder,pLeft+1,pLeft+idx-iLeft,iLeft,idx-1);
+        node->right = build(preorder,inorder,pLeft+idx-iLeft+1,pRight,idx+1,iRight);  
+        return node;
+    }
+};
+
+```
+
+

solution/105.Construct Binary Tree from Preorder and Inorder Traversal/Solution.cpp

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+/**
+ * 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:
+    TreeNode* buildTree(vector<int>& preorder, vector<int>& inorder) {
+        int pRight = preorder.size()-1;
+        int iRight = inorder.size()-1;
+        return build(preorder,inorder,0,pRight,0,iRight);
+    }
+    
+    
+    TreeNode* build(vector<int>& preorder,vector<int>& inorder,int pLeft,int pRight,int iLeft,int iRight){
+        if(pLeft > pRight)return NULL;
+        
+        TreeNode *node = new TreeNode(preorder[pLeft]);
+        int idx = iLeft;
+        
+        while(inorder[idx] != preorder[pLeft])idx++;
+        node->left = build(preorder,inorder,pLeft+1,pLeft+idx-iLeft,iLeft,idx-1);
+        node->right = build(preorder,inorder,pLeft+idx-iLeft+1,pRight,idx+1,iRight);  
+        return node;
+    }
+};