57 lines
1.4 KiB
Markdown
57 lines
1.4 KiB
Markdown
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---
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title: Largest palindrome product
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localeTitle: 最大的回文产品
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---
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## 问题4：最大的回文产品
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### 方法：
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* 回文数字是反转时读取的数字。
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* 从两位3位数的乘积得到的最大数字是`999 * 999` ，所以我们可以制作一个循环，从产生最大数字开始，并检查该数字是否是回文。
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### 解：
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```js
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function largestPalindromeProduct(n) {
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//To get the maximum n digit number, + operator type castes String to Number type
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let max = +[...Array(n)].reduce((a, c) => a+=9, "");
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//Next we get minimum n digit number from the max
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let min = (max+1)/10;
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//To store the result
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let res = [];
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//Starting the loop from max to min
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for (let i = max; i >= min; i--){
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//Another loop
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for (let j = max; j >= min; j--){
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//Getting the product
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let num = i*j;
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//Reversing the number
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let numReverse = [...String(num)].reverse().join('');
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//Checking for palindromic number
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if (num == numReverse) {
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//Pushing the number into array and breaking the loop for efficiency
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res.push(num);
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break;
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}
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}
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}
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// Returning the maximum of the result array
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return Math.max(...res);
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}
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```
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* [运行代码](https://repl.it/@ezioda004/Problem-4-Largest-palindrome-product)
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### 参考文献：
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* [维基百科](https://en.wikipedia.org/wiki/Palindromic_number)
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