Programmer interview golden classic-interview questions 01.01. Determine whether the character is unique

1. Topic introduction

Implement an algorithm to determine whether all characters of a string s are all different.

Example 1:

Input: s = "leetcode"
Output: false 
Example 2:

Input: s = "abc"
Output: true
Limit:

0 <= len(s) <= 100
If you don't use additional data structures, it will be a bonus.

Source: LeetCode
Link: https://leetcode-cn.com/problems/is-unique-lcci
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Two, problem-solving ideas

       This question is easy to implement if the data structure of set is used, so I won't introduce it here. According to restrictions, no additional data structure is applicable. Because the input string consists of all lowercase letters, a character array with a length of 26 is constructed here to record whether each character has appeared. See the code for specific implementation.

Three, problem-solving code

class Solution {
public:
    bool isUnique(string astr) {
        char s[26] = {0};
        for(int i = 0; i < astr.size(); ++i)
        {
            if(s[astr[i] - 'a'] == 1)
                return false;
            s[astr[i] - 'a'] = 1;
        }
        return true;
    }
};

Four, problem-solving results