算法结构与设计基础作业第九周

21.Merge Two Sorted Lists

Description:

Merge two sorted linked lists and return it as a new list. The new list should be made by splicing together the nodes of the first two lists

My C++ code：

/**   * Definition for singly-linked list.   * struct ListNode {   *     int val;  *     ListNode *next;  *     ListNode(int x) : val(x), next(NULL) {}  * };   */ class Solution {     public:         ListNode* mergeTwoLists(ListNode* l1, ListNode* l2) {                 if(nullptr == l1)                 {                         return l2;                              }                          if(nullptr == l2)                {                      return l1;           }                     if(l1->val < l2->val)                 {                         l1->next = mergeTwoLists(l1->next, l2);                         return l1;                }                 else                 {                         l2->next = mergeTwoLists(l1, l2->next);                         return l2;                 }         }  };

100.Same Tree

Description:

Given two binary trees, write a function to check if they are equal or not.

Two binary trees are considered equal if they are structurally identical and the nodes have the same value.

分析：

       题意就是给出两个二叉树，判断是否为相等的二叉树。本题可用递归的思想解决，每个二叉树要么只有一个根，要么就有一个根和一个左子树和一个右子树。左右子树还是二叉树。递归到最后就是判断根结点是否相等了。

My C++ code：

/** * 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:    bool isSameTree(TreeNode* p, TreeNode* q) {        if(nullptr == p && nullptr == q)                 {                         return true;                             }                 else if(nullptr == p || nullptr == q)                 {                        return false;               }                 else                 {                        return p->val == q->val && isSameTree(p->left, q->left) && isSameTree(p->right, q->right);          }    }};