剑指Offer 第1天 第2天

 

第 1 天

栈与队列（简单）

剑指 Offer 09. 用两个栈实现队列

class CQueue {
public:
    CQueue() {}
    
    void appendTail(int value) {
        s1.push(value);
    }
    
    int deleteHead() {
        while(!s1.empty())
        {
            s2.push(s1.top());
            s1.pop();
        }
        int res;
        if(!s2.empty())
        {
            res = s2.top();
            s2.pop();
        }
        else
            return -1;
        while(!s2.empty())
        {
            s1.push(s2.top());
            s2.pop();
        }
        return res;
    }
    stack s1;
    stack s2;
};

剑指 Offer 30. 包含min函数的栈

【解法一】一个栈存放一个结构体结点

typedef struct Node
{
    int num;
    int min;
}Node;
class MinStack {
public:
    /** initialize your data structure here. */
    MinStack() {}
    
    void push(int x) {
        Node a;
        a.num = x;
        a.min = x;
        if(!s.empty() && s.top().min s;
};

【解法二】使用俩个栈

class MinStack {
public:
    /** initialize your data structure here. */
    MinStack() {
    }
    
    void push(int x) {
        num.push(x);
        if(minnum.empty())
        {
           minnum.push(x); 
        }
        else
        {
            if(minnum.top()>=x)
                minnum.push(x);
        }
    }
    
    void pop() {
        if(num.empty())
            return;
        else
        {
            if(num.top()==minnum.top())
                minnum.pop();
            num.pop();
        }
    }
    
    int top() {
        if(!num.empty())
            return num.top();
        return -1;
    }
    
    int min() {
        if(!num.empty())
            return minnum.top();
        return -1;
    }
    stack num;
    stack minnum;
};

第 2 天

链表（简单）

剑指 Offer 06. 从尾到头打印链表

【解法一】使用vector存储，并反转结果

class Solution {
public:
    vector reversePrint(ListNode* head) {
        ListNode* cur = head;
        vector res;
        while(cur)
        {
            res.push_back(cur->val);
            cur = cur->next;
        }
        reverse(res.begin(), res.end());
        return res;
    }
};

【解法二】使用递归思想

class Solution {
public:
    vector res;
    vector reversePrint(ListNode* head) {
        if(!head)
            return res;
        reversePrint(head->next);
        res.push_back(head->val);
        return res;
    }
};

【解法三】使用一个辅助栈

class Solution {
public:
    vector reversePrint(ListNode* head) {
        vector res;
        if(!head)
            return res;
        stack s;
        while(head)
        {
            s.push(head->val);
            head=head->next;
        }
        while(!s.empty())
        {
            res.push_back(s.top());
            s.pop();
        }
        return res;
    }
};

剑指 Offer 24. 反转链表

【解法一】迭代

class Solution {
public:
    ListNode* reverseList(ListNode* head) {
        if(!head)return head;
        ListNode* cur = head;
        ListNode* Next = head;
        ListNode* prev = NULL;
        while(cur)
        {
            Next = cur->next;
            cur->next = prev;
            prev = cur;
            cur = Next;
        }
        return prev;
    }
};

【解法二】递归

class Solution {
public:
    ListNode* recur(ListNode* cur, ListNode* prev)
    {
        if(cur==nullptr)return prev;
        ListNode* res = recur(cur->next, cur);
        cur->next = prev;
        return res;
    }
    ListNode* reverseList(ListNode* head) {
        return recur(head, nullptr);
    }
};

 剑指 Offer 35. 复杂链表的复制