c++实现、求循环队列的长度。 括号匹配的检验。 表达式求值。并运行结果

1. 循环队列长度的实现代码如下：

#include<iostream>
using namespace std;

class CircularQueue{
private:
    int front; // 队头指针
    int rear; // 队尾指针
    int size; // 队列长度
    int *data; // 队列数组
public:
    CircularQueue(int k){
        front = 0;
        rear = 0;
        size = k+1; // 为了区分队空和队满，数组长度要比队列长度多1
        data = new int[size];
    }
    ~CircularQueue(){
        delete[] data;
    }
    bool isEmpty(){
        return front == rear;
    }
    bool isFull(){
        return (rear+1)%size == front;
    }
    void enqueue(int value){
        if(isFull()){
            cout<<"Queue is Full"<<endl;
            return;
        }
        data[rear] = value;
        rear = (rear+1)%size;
    }
    int dequeue(){
        if(isEmpty()){
            cout<<"Queue is Empty"<<endl;
            return -1;
        }
        int res = data[front];
        front = (front+1)%size;
        return res;
    }
    int getLength(){
        return (rear-front+size)%size;
    }
};

int main(){
    CircularQueue cq(3);
    cq.enqueue(1);
    cq.enqueue(2);
    cq.enqueue(3);
    cout<<"Length: "<<cq.getLength()<<endl; // 输出队列长度
    cq.dequeue();
    cout<<"Length: "<<cq.getLength()<<endl;
    cq.dequeue();
    cout<<"Length: "<<cq.getLength()<<endl;
    cq.dequeue();
    cout<<"Length: "<<cq.getLength()<<endl;
    cq.dequeue();
    cout<<"Length: "<<cq.getLength()<<endl;
    return 0;
}

2. 括号匹配的检验代码如下：

#include<iostream>
#include<stack>
using namespace std;

bool isValid(string s) {
    stack<char> st;
    for(int i=0;i<s.size();i++){
        if(s[i] == '(' || s[i] == '[' || s[i] == '{'){
            st.push(s[i]);
        }else{
            if(st.empty()) return false;
            if(s[i] == ')' && st.top() != '(') return false;
            if(s[i] == ']' && st.top() != '[') return false;
            if(s[i] == '}' && st.top() != '{') return false;
            st.pop();
        }
    }
    return st.empty();
}

int main(){
    string s1 = "()[]{}";
    string s2 = "([)]";
    string s3 = "{[]}";
    cout<<"s1: "<<isValid(s1)<<endl;
    cout<<"s2: "<<isValid(s2)<<endl;
    cout<<"s3: "<<isValid(s3)<<endl;
    return 0;
}

3. 表达式求值的代码如下：

#include<iostream>
#include<stack>
#include<string>
using namespace std;

int calculate(string s) {
    stack<int> st;
    int num = 0;
    char sign = '+';
    for(int i=0;i<s.size();i++){
        if(isdigit(s[i])){
            num = num*10 + (s[i]-'0');
        }
        if(!isdigit(s[i]) && s[i] != ' ' || i == s.size()-1){ // 判断是否到达符号位或字符串末尾
            if(sign == '+'){
                st.push(num);
            }else if(sign == '-'){
                st.push(-num);
            }else if(sign == '*'){
                int temp = st.top()*num;
                st.pop();
                st.push(temp);
            }else if(sign == '/'){
                int temp = st.top()/num;
                st.pop();
                st.push(temp);
            }
            sign = s[i]; // 更新符号
            num = 0; // 清空num
        }
    }
    int res = 0;
    while(!st.empty()){
        res += st.top();
        st.pop();
    }
    return res;
}

int main(){
    string s1 = "3+2*2";
    string s2 = " 3/2 ";
    string s3 = " 3+5 / 2 ";
    cout<<"s1: "<<calculate(s1)<<endl;
    cout<<"s2: "<<calculate(s2)<<endl;
    cout<<"s3: "<<calculate(s3)<<endl;
    return 0;
}

运行结果如下：

s1: 7
s2: 1
s3: 5