LeetCodeDay10

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LeetCode232.用栈实现队列

class MyQueue {
private:
    stack<int> s;
    stack<int> buffer;

public:
    MyQueue() {
    }
    
    void push(int x) {
        s.push(x);
    }
    
    int pop() {
        while(!s.empty()){
            int temp = s.top();
            s.pop();
            buffer.push(temp);
        }
        int result = buffer.top();
        buffer.pop();
        while(!buffer.empty()){
            int temp = buffer.top();
            buffer.pop();
            s.push(temp);
        }
        return result;
    }
    
    int peek() {
        while(!s.empty()){
            int temp = s.top();
            s.pop();
            buffer.push(temp);
        }
        int result = buffer.top();
        while(!buffer.empty()){
            int temp = buffer.top();
            buffer.pop();
            s.push(temp);
        }
        return result;
    }
    
    bool empty() {
        return s.empty();
    }
};

/**
 * Your MyQueue object will be instantiated and called as such:
 * MyQueue* obj = new MyQueue();
 * obj->push(x);
 * int param_2 = obj->pop();
 * int param_3 = obj->peek();
 * bool param_4 = obj->empty();
 */

LeetCode225.用队列实现栈

class MyStack {
private:
    queue<int> q;
    queue<int> buffer;

public:
    MyStack() {
    }
    
    void push(int x) {
        q.push(x);
    }
    
    int pop() {
        while(q.size() > 1){
            int temp = q.front();
            q.pop();
            buffer.push(temp);
        }
        int result = q.front();
        q.pop();
        while(!buffer.empty()){
            int temp = buffer.front();
            buffer.pop();
            q.push(temp);
        }
        return result;
    }
    
    int top() {
        while(q.size() > 1){
            int temp = q.front();
            q.pop();
            buffer.push(temp);
        }
        int result = q.front();
        q.pop();
        buffer.push(result);
        while(!buffer.empty()){
            int temp = buffer.front();
            buffer.pop();
            q.push(temp);
        }
        return result;
    }
    
    bool empty() {
        return q.empty();
    }
};

/**
 * Your MyStack object will be instantiated and called as such:
 * MyStack* obj = new MyStack();
 * obj->push(x);
 * int param_2 = obj->pop();
 * int param_3 = obj->top();
 * bool param_4 = obj->empty();
 */

LeetCode20.有效的括号

class Solution {
public:
    bool isValid(string s) {
        stack<char> c_stack;
        for(int i = 0; i < s.length(); i++){
            if(s[i] == '('||s[i] == '[' || s[i] == '{'){
                c_stack.push(s[i]);
            }else if(s[i] == ')'){
                if(!c_stack.empty()&&c_stack.top() == '('){
                    c_stack.pop();
                }else{
                    return false;
                }
            }else if(s[i] == ']'){
                if(!c_stack.empty()&&c_stack.top() == '['){
                    c_stack.pop();
                }else{
                    return false;
                }
            }else if(s[i] == '}'){
                if(!c_stack.empty()&&c_stack.top() == '{'){
                    c_stack.pop();
                }else{
                    return false;
                }
            }
        }
        if(c_stack.empty())
            return true;
        else
            return false;
    }
};

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LeetCode1047.删除字符串中所有相邻重复项

class Solution {
public:
    string removeDuplicates(string s) {
        string result = "";
        stack<char> s_char;
        for(int i = 0; i < s.length(); i++){
            if(s_char.empty()||s_char.top()!=s[i]){
                s_char.push(s[i]);
            }else if(s_char.top() == s[i]){
                s_char.pop();
            }
        }
        while(!s_char.empty()){
            result += s_char.top();
            s_char.pop();
        }
        reverse(result.begin(),result.end());
        return result;
    }
};