problem

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.

submission

// simply emulate stack with a Vec
struct CustomStack {
    inner: Vec<i32>,
    max_size: usize,
}


/** 
 * `&self` means the method takes an immutable reference.
 * If you need a mutable reference, change it to `&mut self` instead.
 */
impl CustomStack {
    fn new(maxSize: i32) -> Self {
        let max_size = maxSize as usize;
        Self {
            inner: Vec::with_capacity(max_size),
            max_size,
        }
    }
    
    fn push(&mut self, x: i32) {
        if self.inner.len() >= self.max_size {
            return;
        }
        self.inner.push(x);
    }
    
    fn pop(&mut self) -> i32 {
        self.inner.pop().unwrap_or(-1)
    }
    
    fn increment(&mut self, k: i32, val: i32) {
        self.inner.iter_mut().take(k as usize).for_each(|mut num| {
            *num += val;
        });
    }
}

/**
 * Your CustomStack object will be instantiated and called as such:
 * let obj = CustomStack::new(maxSize);
 * obj.push(x);
 * let ret_2: i32 = obj.pop();
 * obj.increment(k, val);
 */