https://leetcode-cn.com/problems/design-a-stack-with-increment-operation/
    [制卡]

    1. class CustomStack {
    2.     public arr: number[] = []
    3.     public length: number = 0
    5.     constructor(maxSize: number) {
    6.         this.length = maxSize
    7.     }
    9.     push(x: number): void {
    10.         if (this.arr.length < this.length) {
    11.             this.arr.push(x)
    12.         }
    13.     }
    15.     pop(): number {
    16.         const item = this.arr.pop()
    17.         return item ===  undefined ? -1 : item
    18.     }
    20.     increment(k: number, val: number): void {
    21.        this.arr = this.arr.map((item,index) => index < k? item + val: item);
    22.     }
    23. }