1381. Design a Stack With Increment Operation

Design a stack which supports the following operations.

Implement the CustomStack class:

  • CustomStack(int maxSize) Initializes the object with maxSize which is the maximum number of elements in the stack or do nothing if the stack reached the maxSize.
  • void push(int x) Adds x to the top of the stack if the stack hasn't reached the maxSize.
  • int pop() Pops and returns the top of 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, just 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 customStack = new CustomStack(3); // Stack is Empty []
customStack.push(1);                          // stack becomes [1]
customStack.push(2);                          // stack becomes [1, 2]
customStack.pop();                            // return 2 --> Return top of the stack 2, stack becomes [1]
customStack.push(2);                          // stack becomes [1, 2]
customStack.push(3);                          // stack becomes [1, 2, 3]
customStack.push(4);                          // stack still [1, 2, 3], Don't add another elements as size is 4
customStack.increment(5, 100);                // stack becomes [101, 102, 103]
customStack.increment(2, 100);                // stack becomes [201, 202, 103]
customStack.pop();                            // return 103 --> Return top of the stack 103, stack becomes [201, 202]
customStack.pop();                            // return 202 --> Return top of the stack 102, stack becomes [201]
customStack.pop();                            // return 201 --> Return top of the stack 101, stack becomes []
customStack.pop();                            // return -1 --> Stack is empty return -1.

 

Constraints:

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

Rust Solution

struct CustomStack {
    stack: Vec<i32>,
    inc: Vec<i32>,
    n: usize,
    max_size: usize,
}

impl CustomStack {
    fn new(max_size: i32) -> Self {
        let max_size = max_size as usize;
        let stack = vec![];
        let inc = vec![0; (1 + max_size) as usize];
        let n = 0;
        CustomStack {
            stack,
            inc,
            n,
            max_size,
        }
    }

    fn push(&mut self, x: i32) {
        if self.n != self.max_size {
            self.stack.push(x);
            self.n += 1;
        }
    }

    fn pop(&mut self) -> i32 {
        if let Some(mut top) = self.stack.pop() {
            self.inc[self.n - 1] += self.inc[self.n];
            top += self.inc[self.n];
            self.inc[self.n] = 0;
            self.n -= 1;
            top
        } else {
            -1
        }
    }

    fn increment(&mut self, k: i32, val: i32) {
        let k = k as usize;
        if k > self.n {
            self.inc[self.n] += val;
        } else {
            self.inc[k] += val;
        }
    }
}

#[test]
fn test() {
    let mut stack = CustomStack::new(3);
    stack.push(1);
    stack.push(2);
    assert_eq!(stack.pop(), 2);
    stack.push(2);
    stack.push(3);
    stack.push(4);
    stack.increment(5, 100);
    stack.increment(2, 100);
    assert_eq!(stack.pop(), 103);
    assert_eq!(stack.pop(), 202);
    assert_eq!(stack.pop(), 201);
    assert_eq!(stack.pop(), -1);
}

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