Counter II 計數

Write a function createCounter. It should accept an initial integer init. It should return an object with three functions.

The three functions are:

• increment() increases the current value by 1 and then returns it.
• decrement() reduces the current value by 1 and then returns it.
• reset() sets the current value to init and then returns it.

Example 1:

Input: init = 5, calls = ["increment","reset","decrement"]
Output: [6,5,4]
Explanation:
const counter = createCounter(5);
counter.increment(); // 6
counter.reset(); // 5
counter.decrement(); // 4

Example 2:

Input: init = 0, calls = ["increment","increment","decrement","reset","reset"]
Output: [1,2,1,0,0]
Explanation:
const counter = createCounter(0);
counter.increment(); // 1
counter.increment(); // 2
counter.decrement(); // 1
counter.reset(); // 0
counter.reset(); // 0

Constraints:

-1000 <= init <= 1000
total calls not to exceed 1000

解法:

這是在講建立一個計數器，會給定一個初始值，會指定要回傳一個物件型別為ReturnObj有三個要實作的function

increment → 增加1 回傳當前值

decrement → 減1 回傳當前值

reset → 重設為預設值

把初始值拿一個參數接

並且把操作變數放在這個scope的函式內來做操作

type ReturnObj = {
    increment: () => number,
    decrement: () => number,
    reset: () => number,
}

const createCounter = (init: number) => {
    const initVal = init;
    let val = initVal;
    return {
        increment: () => {
            val += 1;
            return val;
        },
        decrement: () => {
             val -= 1;
            return val;
        },
        reset: () => {
            val = initVal;
            return val;
        },
    } as ReturnObj;
};