100172. Three in One LCCI

难度: Easy

题目描述

Describe how you could use a single array to implement three stacks.

You should implement push(stackNum, value)、pop(stackNum)、isEmpty(stackNum)、peek(stackNum) methods. stackNumvalue is the value that pushed to the stack.

The constructor requires a stackSize parameter, which represents the size of each stack.

Example1:

 Input: 
["TripleInOne", "push", "push", "pop", "pop", "pop", "isEmpty"]
[[1], [0, 1], [0, 2], [0], [0], [0], [0]]
 Output: 
[null, null, null, 1, -1, -1, true]
Explanation: When the stack is empty, `pop, peek` return -1. When the stack is full, `push` does nothing.

Example2:

 Input: 
["TripleInOne", "push", "push", "push", "pop", "pop", "pop", "peek"]
[[2], [0, 1], [0, 2], [0, 3], [0], [0], [0], [0]]
 Output: 
[null, null, null, null, 2, 1, -1, -1]

解题思路

代码实现

解决方案

java

class TripleInOne {

    private Integer[][] stack;
    private int stackSize;

    public TripleInOne(int stackSize) {
        this.stackSize = stackSize;
        this.stack = new Integer[3][stackSize];
    }

    public void push(int stackNum, int value) {
        if (stackNum < 0) {
            return;
        }

        Integer[] data = stack[stackNum];
        for (int i = 0; i < data.length; i++) {
            if (data[i] == null) {
                data[i] = value;
                break;
            }
        }
    }

    public int pop(int stackNum) {
        if (stackNum < 0) {
            return -1;
        }
        Integer[] data = stack[stackNum];
        for (int i = data.length - 1; i > -1; i--) {
            if (data[i] != null) {

                int res = data[i];
                data[i] = null;
                return res;

            }
        }
        return -1;
    }

    public int peek(int stackNum) {
        if (stackNum < 0) {
            return -1;
        }
        Integer[] data = stack[stackNum];
        for (int i = data.length - 1; i > -1; i--) {
            if (data[i] != null) {

                int res = data[i];
                return res;

            }
        }
        return -1;
    }

    public boolean isEmpty(int stackNum) {
        if (stackNum < 0) {
            return true;
        }
        Integer[] data = stack[stackNum];
        if(data==null|| data.length==0){
            return true;
        }
        return data[0] == null;
    }
}

/**
 * Your TripleInOne object will be instantiated and called as such:
 * TripleInOne obj = new TripleInOne(stackSize);
 * obj.push(stackNum,value);
 * int param_2 = obj.pop(stackNum);
 * int param_3 = obj.peek(stackNum);
 * boolean param_4 = obj.isEmpty(stackNum);
 */