基础算法——堆栈

/*************************************************************************
    > File Name: stack_queue.cpp
    > Author: xinyang
    > Mail: xuechen.xy@gmail.com 
    > Created Time: Wed 07 Oct 2015 02:24:43 PM CST
 ************************************************************************/

#include <iostream>
#include <stack>
#include <queue>
#include <vector>
#include <deque>
using namespace std;

/*
 * 用两个栈实现队列
 */
template <typename T>
class CQueue {
public:
    CQueue() {
    }
    ~CQueue() {
    }

    void append_to_tail(const T &node);
    T delete_head();
private:
    stack<T> stack1;
    stack<T> stack2;
};

template <typename T>
void CQueue<T>::append_to_tail(const T&element) {
    stack1.push(element);
}

template <typename T>
T CQueue<T>::delete_head() {
    if (stack2.empty()) {
        while (!stack1.empty()) {
            T x = stack1.top();
            stack1.pop();
            stack2.push(x);
        }
    }
    if (stack2.empty()) {
        cout << "queue is empty" << endl;
        return 0;
    }
    T head = stack2.top();
    stack2.pop();
    return head;
}

/*
 * 包含min函数的栈
 */
template <typename T>
class StackWithMin {
public:
    void push(const T &value);
    void pop();
    const T &get_min() const;
private:
    stack<T> m_data;
    stack<T> m_min;
};

template <typename T>
void StackWithMin<T>::push(const T &value) {
    m_data.push(value);
    if (m_min.empty() || value < m_min.top()) {
        m_min.push(value);
    } else {
        m_min.push(m_min.top());
    }
}

template <typename T>
void StackWithMin<T>::pop() {
    if (m_data.empty() || m_min.empty()) {
        cout << "stack is empty" << endl;
        return;
    }
    m_data.pop();
    m_min.pop();
}

template <typename T>
const T &StackWithMin<T>::get_min() const {
    if (m_data.empty() && m_min.empty()) {
        cout << "stack is empty" << endl;
    }
    return m_min.top();
}

/*
 * 给出入栈顺序，判断所给出栈序列是否合法
 */
bool is_pop_order(const int push[], const int pop[], int n) {
    if (push == NULL || pop == NULL || n <= 0) {
        return false;
    }

    bool possible = false;
    int idx_push = 0, idx_pop = 0;
    stack<int> S;
    while (idx_pop < n) {
        // 找到栈顶与当前pop序列值一致的位置
        while (S.empty() || S.top() != pop[idx_pop]) {
            if (idx_push == n) {
                break;
            }
            S.push(push[idx_push]);
            ++idx_push;
        }
        if (S.top() != pop[idx_pop]) {
            break;
        }
        S.pop();
        ++idx_pop;
    }
    if (S.empty() && idx_pop == n) {
        possible = true;
    }
    return possible;
}
        
/*
 * 滑动窗口的最大值
 */
vector<int> max_in_windows(const int A[], unsigned int n, unsigned int size) {
    vector<int> ret;
    if (A == NULL || n <= 0 || size <= 0 || size > n) {
        return ret;
    }

    deque<int> index;
    for (int i = 0; i < size; ++i) {
        while (!index.empty() && A[i] >= A[index.back()]) {
            index.pop_back();
        }
        index.push_back(i);
    }

    for (int i = size; i < n; ++i) {
        ret.push_back(A[index.front()]);
        while (!index.empty() && A[i] >= A[index.back()]) {
            index.pop_back();
        }
        if (!index.empty() && index.front() <= (int)(i - size)) {
            index.pop_front();
        }
        index.push_back(i);
    }
    ret.push_back(A[index.front()]);
    return ret;
}

int main() {
    cout << "implete a queue with two stacks" << endl;
    CQueue<int> *CQ = new CQueue<int>();
    CQ->append_to_tail(0);
    CQ->append_to_tail(1);
    cout << CQ->delete_head() << endl << endl;

    cout << "implete a stack with minimum" << endl;
    StackWithMin<int> *SWM = new StackWithMin<int>();
    SWM->push(1);
    SWM->push(2);
    cout << SWM->get_min() << endl;
    SWM->pop();
    SWM->push(0);
    cout << SWM->get_min() << endl << endl;

    int A[] = {1, 2, 3, 4, 5};
    // int B[] = {4, 5, 3, 2, 1};
    int B[] = {4, 3, 5, 1, 2};
    if (true == is_pop_order(A, B, 5)) {
        cout << "is pop order" << endl << endl;
    } else {
        cout << "is not pop order" << endl << endl;
    }

    vector<int> ret = max_in_windows(A, 5, 3);
    for (int i = 0; i < ret.size(); ++i) {
        cout << ret[i] << ' ';
    }
    cout << endl << endl;

    return 0;
}