js 判断是否为回文数
```javascript
function palindrome(str) {
// Step 1. The first part is the same as earlier
var re = /[^A-Za-z0-9]/g; // or var re = /[\W_]/g;
str = str.toLowerCase().replace(re, '');
// Step 2. Create the FOR loop
var len = str.length; // var len = "A man, a plan, a canal. Panama".length = 30
for (var i = 0; i < len/2; i++) {
if (str[i] !== str[len - 1 - i]) { // As long as the characters from each part match, the FOR loop will go on
return false; // When the characters don't match anymore, false is returned and we exit the FOR loop
}
```
yihong0618
slice() works like substring() with a few different behaviors.
Syntax: string.slice(start, stop);
Syntax: string.substring(start, stop);
What they have in common:
If start equals stop: returns an empty string
If stop is omitted: extracts characters to the end of the string
If either argument is greater than the string's length, the string's length will be used instead.
Distinctions of substring():
If start > stop, then substring will swap those 2 arguments.
If either argument is negative or is NaN, it is treated as if it were 0.
Distinctions of slice():
If start > stop, slice() will return the empty string. ("")
If start is negative: sets char from the end of string, exactly like substr() in Firefox. This behavior is observed in both Firefox and IE.
If stop is negative: sets stop to: string.length – Math.abs(stop) (original value), except bounded at 0 (thus, Math.max(0, string.length + stop)) as covered in the ECMA specification.
Source: Rudimentary Art of Programming & Development: Javascript: substr() v.s. substring()
yihong0618
let arr = new Array(m).fill(Array(n).fill(1).....
这个东西是浅拷贝，必须用深拷贝，妈的
let m = Array.from({length: 6}, e => Array(12).fill(0));
在 js中 [1] in [[1,2], [1], [1,2,3]] 无论是includes 还是indexof都不好用。
splice() 方法通过删除或替换现有元素或者原地添加新的元素来修改数组,并以数组形式返回被修改的内容。此方法会改变原数组。 ```javascript //从第 2 位开始删除 0 个元素，插入“drum” var myFish = ["angel", "clown", "mandarin", "sturgeon"]; var removed = myFish.splice(2, 0, "drum"); //从第 2 位开始删除 0 个元素，插入“drum” 和 "guitar" var myFish = ['angel', 'clown', 'mandarin', 'sturgeon']; var removed = myFish.splice(2, 0, 'drum', 'guitar'); // 从第 3 位开始删除 1 个元素 var myFish = ['angel', 'clown', 'drum', 'sturgeon']; var removed = myFish.splice(2, 1, "trumpet") ```
js 判断是否为回文数 ```javascript function palindrome(str) { // Step 1. The first part is the same as earlier var re = /[^A-Za-z0-9]/g; // or var re = /[\W_]/g; str = str.toLowerCase().replace(re, ''); // Step 2. Create the FOR loop var len = str.length; // var len = "A man, a plan, a canal. Panama".length = 30 for (var i = 0; i < len/2; i++) { if (str[i] !== str[len - 1 - i]) { // As long as the characters from each part match, the FOR loop will go on return false; // When the characters don't match anymore, false is returned and we exit the FOR loop } ```
slice() works like substring() with a few different behaviors. Syntax: string.slice(start, stop); Syntax: string.substring(start, stop); What they have in common: If start equals stop: returns an empty string If stop is omitted: extracts characters to the end of the string If either argument is greater than the string's length, the string's length will be used instead. Distinctions of substring(): If start > stop, then substring will swap those 2 arguments. If either argument is negative or is NaN, it is treated as if it were 0. Distinctions of slice(): If start > stop, slice() will return the empty string. ("") If start is negative: sets char from the end of string, exactly like substr() in Firefox. This behavior is observed in both Firefox and IE. If stop is negative: sets stop to: string.length – Math.abs(stop) (original value), except bounded at 0 (thus, Math.max(0, string.length + stop)) as covered in the ECMA specification. Source: Rudimentary Art of Programming & Development: Javascript: substr() v.s. substring()
let arr = new Array(m).fill(Array(n).fill(1)..... 这个东西是浅拷贝，必须用深拷贝，妈的 let m = Array.from({length: 6}, e => Array(12).fill(0));
嵌套数组如何set 和判断是否在数组中 1. 先排序 2. Array.from(new Set(result.map(JSON.stringify)), JSON.parse)