LeetCode 1381. Design a Stack With Increment Operation

Question

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.

https://leetcode.com/problems/design-a-stack-with-increment-operation/

class CustomStack {
    int n;
    int[] inc;
    Stack<Integer> stack = new Stack<>();
    public CustomStack(int maxSize) {
        n = maxSize;
        inc = new int[n];
    }
    
    public void push(int x) {
        if(stack.size()<n) stack.push(x);
    }
    
    public int pop() {
        int i = stack.size()-1;
        if(i<0) return -1;
        if(i>0) inc[i-1] += inc[i];
        int res = stack.pop() + inc[i];
        inc[i] = 0;
        return res;
    }
    
    public void increment(int k, int val) {
        int i = Math.min(k, stack.size()) - 1;
        if(i >= 0) inc[i] += val;
    }
}