LeetCode interview questions 03.01. Three in one

1. Topic

  triple. Describe how to implement three stacks using only one array.

  You should implement push(stackNum, value)、pop(stackNum)、isEmpty(stackNum)、peek(stackNum)method. stackNumRepresents the stack subscript, valuerepresenting the pushed value.

  The constructor will pass in a stackSizeparameter representing the size of each stack.

  Click here to jump to the topic .

Example 1:

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: return -1 when the stack is empty , and not press pop, peekwhen the stack is full pushinto the element.

Example 2:

输入：
[“TripleInOne”, “push”, “push”, “push”, “pop”, “pop”, “pop”, “peek”]
[[2], [0, 1], [0, 2], [0, 3], [0], [0], [0], [0]]
输出：
[null, null, null, null, 2, 1, -1, -1]

hint:

• 0 <= stackNum <= 2

2. C# solution

  Very basic topic, the code is as follows:

public class TripleInOne {
    
    
    private int[][] stack; // 2 维数组存储 3 个栈
    private int[] p;       // 1 维数组存储 3 个栈的指针

    public TripleInOne(int stackSize) {
    
    
        stack = new int[3][];
        for (int i = 0; i < 3; i++) {
    
    
            stack[i] = new int[stackSize];
        }
        p = new int[] {
    
    -1, -1, -1};
    }
    
    public void Push(int stackNum, int value) {
    
    
        if (p[stackNum] == stack[stackNum].Length - 1) return;
        stack[stackNum][++p[stackNum]] = value;
    }
    
    public int Pop(int stackNum) {
    
    
        if (p[stackNum] == -1) return -1;
        return stack[stackNum][p[stackNum]--];
    }
    
    public int Peek(int stackNum) {
    
    
        if (p[stackNum] == -1) return -1;
        return stack[stackNum][p[stackNum]];
    }
    
    public bool IsEmpty(int stackNum) {
    
    
        return p[stackNum] == -1;
    }
}

/**
 * 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);
 * bool param_4 = obj.IsEmpty(stackNum);
 */

• Time Complexity: None.
• Space Complexity: None.