棧和隊列--letcode應用

上一篇少一個main 方法測試，這次補上

main

public class Main {

    public static void main(String[] args) {

        ArrayStack<Integer> stack = new ArrayStack<>();

        for(int i = 0 ; i < 5 ; i ++){
            stack.push(i);
            System.out.println(stack);
        }

        stack.pop();
        System.out.println(stack);
    }
}

接着說letcode上的應用：括號匹配問題

思路：先將左括號入棧，然後跟右括號對比，比對上就出棧，並且比對下一個，如果比對完了都正確且沒有剩餘括號則正確

class Solution {

    public boolean isValid(String s) {

        Stack<Character> stack = new Stack<>();
        for(int i = 0 ; i < s.length() ; i ++){
            char c = s.charAt(i);
            if(c == '(' || c == '[' || c == '{')
                stack.push(c);
            else{
                if(stack.isEmpty())
                    return false;

                char topChar = stack.pop();
                if(c == ')' && topChar != '(')
                    return false;
                if(c == ']' && topChar != '[')
                    return false;
                if(c == '}' && topChar != '{')
                    return false;
            }
        }
        return stack.isEmpty();
    }

    public static void main(String[] args) {

        System.out.println((new Solution()).isValid("()[]{}"));
        System.out.println((new Solution()).isValid("([)]"));
    }
}

用自己實現的棧提交，將用到的類作爲內部類提交。（複製到lecode上即可）

具體實現創建Solution.java

class Solution {

    public boolean isValid(String s) {

        ArrayStack<Character> stack = new ArrayStack<>();
        for(int i = 0 ; i < s.length() ; i ++){
            char c = s.charAt(i);
            if(c == '(' || c == '[' || c == '{')
                stack.push(c);
            else{
                if(stack.isEmpty())
                    return false;

                char topChar = stack.pop();
                if(c == ')' && topChar != '(')
                    return false;
                if(c == ']' && topChar != '[')
                    return false;
                if(c == '}' && topChar != '{')
                    return false;
            }
        }
        return stack.isEmpty();
    }

    public static void main(String[] args) {

        System.out.println((new Solution()).isValid("()[]{}"));
        System.out.println((new Solution()).isValid("([)]"));
    }
}