Golden code of programmer interview

Interview questions 01.01. Determine whether the character is unique
Implement an algorithm , Determine a string s Whether all the characters of are different .
Example 1：
Input : s = “leetcode”
Output : false
Example 2：
Input : s = “abc”
Output : true

set Weight removal comparison length

/** * @param {string} astr * @return {boolean} */
var isUnique = function(astr) {
    
    return new Set(astr).size==astr.length
};

Hash thought

/** * @param {string} astr * @return {boolean} */
var isUnique = function(astr) {
    
    let obj = {
    }
    for (let i of astr) {
    
        if (obj[i]) {
    
            return false
        } else {
    
            obj[i] = 1
        }
    }
    return true
}    

First and last index Is it consistent

/** * @param {string} astr * @return {boolean} */
var isUnique = function(astr) {
    
 for (let i of astr) {
    
        if (astr.indexOf(i) !== astr.lastIndexOf(i)) {
    
            return false
        }
    }
    return true
}