Question

方法sortStack()按降序排列未排序的堆栈。但是，当我尝试将方法用于2个单独的堆栈时，第二个排序的堆栈将与第一个排序的堆栈合并。有人可以帮我解决我所缺少的吗？

    static Stack<Integer> descending = new Stack<Integer>();
    static Stack<Integer> tmpStack = new Stack<Integer>();

    public static Stack<Integer> sortStack(Stack<Integer> input){

    while(!input.isEmpty()) {
        int tmp = input.pop();
        while(!tmpStack.isEmpty() && tmpStack.peek() > tmp) {
            input.push(tmpStack.pop());
        }
        tmpStack.push(tmp);
    }

    while(!tmpStack.isEmpty()) {
        descending.push(tmpStack.pop());
    }
    return descending;
}

public static void main(String args[]){

            Stack<Integer> A = new Stack<Integer>(); 
            A.push(34); 
            A.push(3); 
            A.push(31);

            System.out.println("unsorted: " + A);
            Stack<Integer> C = sortStack(A);
            System.out.println("sorted: " + C);

            Stack<Integer> B = new Stack<Integer>();
            B.push(1); 
            B.push(12); 
            B.push(23);

            System.out.println("unsorted: " + B);
            Stack<Integer> D = sortStack(B);
            System.out.println("sorted: " + D);        
        }

输出

unsorted: [34, 3, 31]

sorted: [34, 31, 3]

unsorted: [1, 12, 23]

sorted: [34, 31, 3, 23, 12, 1]

Answer 1

public static Stack<Integer> sortStack(Stack<Integer> stack) {
    stack.sort(Comparator.reverseOrder());
    return stack;
}

输出：

unsorted: [34, 3, 31]
sorted: [34, 31, 3]
unsorted: [1, 12, 23]
sorted: [23, 12, 1]

Answer 2

将Stack<Integer> tmpStack = new Stack<Integer>();声明为局部变量而不是类变量。

public static void main(String args[]){

            Stack<Integer> A = new Stack<Integer>(); 
            A.push(34); 
            A.push(3); 
            A.push(31);

            System.out.println("unsorted: " + A);
            Stack<Integer> C = sortStack(A);
//After this method call tmpStack will have [3, 31, 34]
            System.out.println("sorted: " + C);

            Stack<Integer> B = new Stack<Integer>();
            B.push(1); 
            B.push(12); 
            B.push(23);

            System.out.println("unsorted: " + B);
            Stack<Integer> D = sortStack(B);
//After this method call tmpStack will have [34, 31, 3, 1, 12, 23]
//Here you are appending 1, 12, 23 values to existing tmpStack[3, 31, 34]
            System.out.println("sorted: " + D);        
        }

解决方案：

将tmpStack声明为局部变量。

此外，如果您想按降序排序，则无需添加额外的代码

while(!tmpStack.isEmpty()) {
    descending.push(tmpStack.pop());
}

您只需将条件更改为'>'或'<'

升序：while(!tmpStack.isEmpty() && tmpStack.peek() > tmp) {}

取消顺序：while(!tmpStack.isEmpty() && tmpStack.peek() < tmp) {}

public static Stack<Integer> sortStack(Stack<Integer> input) {

    Stack<Integer> tmpStack = new Stack<Integer>();

    while (!input.isEmpty()) {
        int tmp = input.pop();
        while (!tmpStack.isEmpty() && tmpStack.peek() < tmp) {
            input.push(tmpStack.pop());
        }
        tmpStack.push(tmp);
    }

    //while (!tmpStack.isEmpty()) {
    //  descending.push(tmpStack.pop());
    //}
    return tmpStack;
}

已排序的堆栈在主要方法处被合并

2 个答案: