93 lines
2.0 KiB
Markdown
93 lines
2.0 KiB
Markdown
# 毎日一题 - 9. Palindrome number
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## 信息卡片
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- 时间：2019-07-25
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- 题目链接：https://leetcode.com/problems/palindrome-number/submissions/
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- tag：`Math`
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## 题目描述
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```
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Determine whether an integer is a palindrome. An integer is a palindrome when it reads the same backward as forward.
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Example 1:
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Input: 121
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Output: true
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Example 2:
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Input: -121
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Output: false
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Explanation: From left to right, it reads -121. From right to left, it becomes 121-. Therefore it is not a palindrome.
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Example 3:
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Input: 10
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Output: false
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Explanation: Reads 01 from right to left. Therefore it is not a palindrome.
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Follow up:
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Coud you solve it without converting the integer to a string?
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```
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## 参考答案
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转成字符串方式
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1. 负数都是非回文数，10的整数倍不是回文。
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2. 将数字转为字符串，再逆序排列字符串。两者比较，相等就是回文数。
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直接操作整数方式
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1. 复制x到temp;
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2. 取temp末尾数字，方式为temp与10的求余；组成新数reverse;
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3. 每取完一位,temp缩小10倍并且去掉小数。
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4. reverse要`先扩大十倍`再加上取下来的数
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5. 当temp === 0时，表示已经取完；reverse与x比较
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参考JavaScript代码：
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```js
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/**
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* @param {number} x
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* @return {boolean}
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* 转成字符串
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*/
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var isPalindrome = function(x) {
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if(x < 0 ) return false;
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if(x === 0) return true;
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if(x % 10 === 0) return false;
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let reverse = '';
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let str = String(x);
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for(let i = str.length - 1; i >= 0; i--) {
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reverse += str[i]
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}
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return str === reverse
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};
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/**
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* @param {number} x
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* @return {boolean}
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* 不转成字符串
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*/
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var isPalindrome = function(x) {
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if(x < 0 ) return false;
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if(x === 0) return true;
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if(x % 10 === 0) return false;
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let temp = x;
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let reverse = 0;
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while(temp > 0) {
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let num = temp % 10;
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temp = (temp - num)/10; // 或 temp = (temp / 10) >> 0,去除小数位
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reverse = reverse * 10 + num
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}
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return x === reverse
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};
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```
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## 优秀解答
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> 暂缺
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