字符串按字符出现频次排序

 "Aacbbcc"  输出 "cccbbAa"

const s = "Aacbbcc"function setString(string) {const map = new Map();let res = ''for(let char of string){const val = map.get(char)map.set(char, val?val +1:1)}const arr = Array.from(map).sort((a,b) =>b[1] - a[1])for( const [char, count] of arr){res += char.repeat(count)}return res
}const sortedString = setString(s)
console.log(sortedString);

js计字符串中字母出现的次数，例如adkhhq， 返回 {a:1,d:1,k:1h:2,a:1}
 

function countStr(str) {const obj = {};for (let i = 0; i < str.length; i++) {let key = str[i]if (!obj[key]) {obj[key] = 1} else {obj[key]++}}return obj
}console.log(countStr("adkhhq"))

js去掉字符串中不相邻的重复字符串 例如 aabcad 结果为aabcd

js 返回无序数组中第一个不重复的数字

function findFirstUnique(numbers) {const seen = new Set();for (const num of numbers) {if (seen.has(num)) {seen.delete(num);} else {seen.add(num);}}return [...seen.values()][0];
}// 示例
const numbers = [2, 1, 3, 3, 2];
const unique = findFirstUnique(numbers);
console.log(unique);  // 输出 1