Question

1381. Design a Stack With Increment Operation

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Description

Design a stack that supports increment operations on its elements.

Implement the CustomStack class:

• CustomStack(int maxSize) Initializes the object with maxSize which is the maximum number of elements in the stack.
• void push(int x) Adds x to the top of the stack if the stack has not reached the maxSize.
• int pop() Pops and returns the top of the stack or -1 if the stack is empty.
• void inc(int k, int val) Increments the bottom k elements of the stack by val. If there are less than k elements in the stack, increment all the elements in the stack.

 

Example 1:

Input
["CustomStack","push","push","pop","push","push","push","increment","increment","pop","pop","pop","pop"]
[[3],[1],[2],[],[2],[3],[4],[5,100],[2,100],[],[],[],[]]
Output
[null,null,null,2,null,null,null,null,null,103,202,201,-1]
Explanation
CustomStack stk = new CustomStack(3); // Stack is Empty []
stk.push(1);              // stack becomes [1]
stk.push(2);              // stack becomes [1, 2]
stk.pop();              // return 2 --> Return top of the stack 2, stack becomes [1]
stk.push(2);              // stack becomes [1, 2]
stk.push(3);              // stack becomes [1, 2, 3]
stk.push(4);              // stack still [1, 2, 3], Do not add another elements as size is 4
stk.increment(5, 100);        // stack becomes [101, 102, 103]
stk.increment(2, 100);        // stack becomes [201, 202, 103]
stk.pop();              // return 103 --> Return top of the stack 103, stack becomes [201, 202]
stk.pop();              // return 202 --> Return top of the stack 202, stack becomes [201]
stk.pop();              // return 201 --> Return top of the stack 201, stack becomes []
stk.pop();              // return -1 --> Stack is empty return -1.

 

Constraints:

• 1 <= maxSize, x, k <= 1000
• 0 <= val <= 100
• At most 1000 calls will be made to each method of increment, push and pop each separately.

Solutions

Solution 1: Array Simulation

We can use an array $stk$ to simulate the stack, and an integer $i$ to represent the position of the next element to be pushed into the stack. In addition, we need another array $add$ to record the cumulative increment value at each position.

When calling $push(x)$, if $i < maxSize$, we put $x$ into $stk[i]$ and increment $i$ by one.

When calling $pop()$, if $i \leq 0$, it means the stack is empty, so we return $-1$. Otherwise, we decrement $i$ by one, and the answer is $stk[i] + add[i]$. Then we add $add[i]$ to $add[i - 1]$, and set $add[i]$ to zero. Finally, we return the answer.

When calling $increment(k, val)$, if $i > 0$, we add $val$ to $add[\min(i, k) - 1]$.

The time complexity is $O(1)$, and the space complexity is $O(n)$. Where $n$ is the maximum capacity of the stack.

class CustomStack:
  def __init__(self, maxSize: int):
    self.stk = [0] * maxSize
    self.add = [0] * maxSize
    self.i = 0

  def push(self, x: int) -> None:
    if self.i < len(self.stk):
      self.stk[self.i] = x
      self.i += 1

  def pop(self) -> int:
    if self.i <= 0:
      return -1
    self.i -= 1
    ans = self.stk[self.i] + self.add[self.i]
    if self.i > 0:
      self.add[self.i - 1] += self.add[self.i]
    self.add[self.i] = 0
    return ans

  def increment(self, k: int, val: int) -> None:
    i = min(k, self.i) - 1
    if i >= 0:
      self.add[i] += val


# Your CustomStack object will be instantiated and called as such:
# obj = CustomStack(maxSize)
# obj.push(x)
# param_2 = obj.pop()
# obj.increment(k,val)

class CustomStack {
  private int[] stk;
  private int[] add;
  private int i;

  public CustomStack(int maxSize) {
    stk = new int[maxSize];
    add = new int[maxSize];
  }

  public void push(int x) {
    if (i < stk.length) {
      stk[i++] = x;
    }
  }

  public int pop() {
    if (i <= 0) {
      return -1;
    }
    int ans = stk[--i] + add[i];
    if (i > 0) {
      add[i - 1] += add[i];
    }
    add[i] = 0;
    return ans;
  }

  public void increment(int k, int val) {
    if (i > 0) {
      add[Math.min(i, k) - 1] += val;
    }
  }
}

/**
 * Your CustomStack object will be instantiated and called as such:
 * CustomStack obj = new CustomStack(maxSize);
 * obj.push(x);
 * int param_2 = obj.pop();
 * obj.increment(k,val);
 */

class CustomStack {
public:
  CustomStack(int maxSize) {
    stk.resize(maxSize);
    add.resize(maxSize);
    i = 0;
  }

  void push(int x) {
    if (i < stk.size()) {
      stk[i++] = x;
    }
  }

  int pop() {
    if (i <= 0) {
      return -1;
    }
    int ans = stk[--i] + add[i];
    if (i > 0) {
      add[i - 1] += add[i];
    }
    add[i] = 0;
    return ans;
  }

  void increment(int k, int val) {
    if (i > 0) {
      add[min(k, i) - 1] += val;
    }
  }

private:
  vector<int> stk;
  vector<int> add;
  int i;
};

/**
 * Your CustomStack object will be instantiated and called as such:
 * CustomStack* obj = new CustomStack(maxSize);
 * obj->push(x);
 * int param_2 = obj->pop();
 * obj->increment(k,val);
 */

type CustomStack struct {
  stk []int
  add []int
  i   int
}

func Constructor(maxSize int) CustomStack {
  return CustomStack{make([]int, maxSize), make([]int, maxSize), 0}
}

func (this *CustomStack) Push(x int) {
  if this.i < len(this.stk) {
    this.stk[this.i] = x
    this.i++
  }
}

func (this *CustomStack) Pop() int {
  if this.i <= 0 {
    return -1
  }
  this.i--
  ans := this.stk[this.i] + this.add[this.i]
  if this.i > 0 {
    this.add[this.i-1] += this.add[this.i]
  }
  this.add[this.i] = 0
  return ans
}

func (this *CustomStack) Increment(k int, val int) {
  if this.i > 0 {
    this.add[min(k, this.i)-1] += val
  }
}

/**
 * Your CustomStack object will be instantiated and called as such:
 * obj := Constructor(maxSize);
 * obj.Push(x);
 * param_2 := obj.Pop();
 * obj.Increment(k,val);
 */

class CustomStack {
  private stk: number[];
  private add: number[];
  private i: number;

  constructor(maxSize: number) {
    this.stk = Array(maxSize).fill(0);
    this.add = Array(maxSize).fill(0);
    this.i = 0;
  }

  push(x: number): void {
    if (this.i < this.stk.length) {
      this.stk[this.i++] = x;
    }
  }

  pop(): number {
    if (this.i <= 0) {
      return -1;
    }
    const ans = this.stk[--this.i] + this.add[this.i];
    if (this.i > 0) {
      this.add[this.i - 1] += this.add[this.i];
    }
    this.add[this.i] = 0;
    return ans;
  }

  increment(k: number, val: number): void {
    if (this.i > 0) {
      this.add[Math.min(this.i, k) - 1] += val;
    }
  }
}

/**
 * Your CustomStack object will be instantiated and called as such:
 * var obj = new CustomStack(maxSize)
 * obj.push(x)
 * var param_2 = obj.pop()
 * obj.increment(k,val)
 */