技術標籤：前端佇列字串javascriptjs

什麼是迴文

迴文是正反都能讀通的單詞，片語，數或一些列字元的序列，例如 madam 與 racecar。

如何實現迴文檢查其的功能

如上所述，迴文是一些正反顛倒都能和之前的值一樣的序列。那麼我們只需要抽出第一位與最後一位，第二位與倒數第二位來對比即可。

class Deque {
    constructor() {
        this.count = 0;
        this.lowestCount = 0;
        this.items = {};
    }
    
    size() { return  this
 
.count - this.lowestCount; }

    addFront(element) {
        if ( this.isEmpty() ) this.addBack(element);
        else if ( this.lowestCount > 0 ) {
            this.lowestCount--;
            this.items[this.lowestCount] = element;
        } else {
            for ( let i = this.count; i > 0; i--
 
 ) this.items[i] = this.items[i - 1];
            this.count++;
            this.lowestCount = 0;
            this.items[0] = element;
        }
    }

    addBack(element) {
        this.items[this.count] = element;
        this.count++;
    }

    removeFront() {
        if ( this.isEmpty() ) return
 
 undefined;

        const result = this.items[this.lowestCount];
        delete this.items[this.lowestCount];
        this.lowestCount++;
        return result;
    }

    removeBack() {
        if ( this.isEmpty() ) return undefined;

        this.count--;
        const result = this.items[this.count];
        delete this.items[this.count];
        return result;
    }
}

/**
* 驗證該序列是否為迴文
 * @param {String} palindrome 
 */
const PalindromeChecker = palindrome => {
    if ( palindrome === undefined || palindrome === null || palindrome !== null && palindrome.length === 0 ) 
        return false;// 判定扔進來的字元（序列）是否為 null，undefined，以及空字串

    const deque = new Deque();// 例項化一個雙端佇列類
    const stringArr = palindrome.toLocaleLowerCase().split(" ").join("");// 將字串重新整理（無空格）

    let isEqual = true,// 判定是否為迴文的關鍵值
        firstChar , lastChar;

    for ( let i = 0; i < stringArr.length; i++ ) 
        deque.addBack(stringArr.charAt(i));// 將字串傳遞給雙端佇列類

    while (deque.size() > 1 && isEqual) {// 迴圈判斷
        firstChar = deque.removeFront();
        lastChar = deque.removeBack();

        if ( firstChar !== lastChar ) isEqual = false;
    }

    return isEqual;
}