面试题50. 第一个只出现一次的字符

男娘i 2023-02-18 03:22 84阅读 0赞

# 题目： #

[面试题50. 第一个只出现一次的字符][50.]  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3p5eF9seQ_size_16_color_FFFFFF_t_70]

# 题解： #

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3p5eF9seQ_size_16_color_FFFFFF_t_70 1]

## 1. 题解一：哈希表 ##

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3p5eF9seQ_size_16_color_FFFFFF_t_70 2]  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3p5eF9seQ_size_16_color_FFFFFF_t_70 3]  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3p5eF9seQ_size_16_color_FFFFFF_t_70 4]  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3p5eF9seQ_size_16_color_FFFFFF_t_70 5]  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3p5eF9seQ_size_16_color_FFFFFF_t_70 6]

## 2. 题解二：使用数组代替哈希表计数 ##

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3p5eF9seQ_size_16_color_FFFFFF_t_70 7]  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3p5eF9seQ_size_16_color_FFFFFF_t_70 8]

# 代码： #

## 1. 代码一：哈希表 ##

import java.util.*;
    
    public class 面试题50 { 
    
        // 方法1：哈希表
        public static char firstUniqChar(String s) { 
            HashMap<Character, Boolean> map = new HashMap<>();
            char c[] = s.toCharArray();
            for(int i = 0; i < c.length; i++)
            { 
                if(map.containsKey(c[i]))
                { 
                    map.put(c[i], false);
                }
                else
                { 
                    map.put(c[i], true);
                }
            }
            for(int i = 0; i < c.length; i++)
            { 
                if(map.get(c[i]) == true)
                { 
                    return c[i];
                }
            }
            return ' ';
        }
        
        public static void main(String[] args) { 
            String str = "abaccdeff";
            char res = firstUniqChar(str);
            System.out.println(res);
        }
    }

## 2. 代码二：使用数组代替哈希表计数 ##

import java.util.*;
    
    public class 面试题50 { 
    
        // 方法2：使用数组代替哈希表计数
        public static char firstUniqChar(String s) { 
            int count[] = new int[26];
            char c[] = s.toCharArray();
            for(int i = 0; i < c.length; i++)
            { 
                count[c[i] - 'a']++;
            }
            for(int i = 0; i < c.length; i++)
            { 
                if(count[c[i] - 'a'] == 1)
                { 
                    return c[i];
                }
            }
            return ' ';
        }    
        
        public static void main(String[] args) { 
            String str = "abaccdeff";
            char res = firstUniqChar(str);
            System.out.println(res);
        }
    }

# 参考： #

1.  [面试题50. 第一个只出现一次的字符（哈希表 / 有序哈希表，清晰图解）][50. _ _]
2.  [面试题50.java 使用数组代替哈希表计数（打败99.9%）][50.java _99.9]
3.  [一个简单高效的统计方法][Link 1]

[50.]: https://leetcode-cn.com/problems/di-yi-ge-zhi-chu-xian-yi-ci-de-zi-fu-lcof/
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[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3p5eF9seQ_size_16_color_FFFFFF_t_70 1]: https://img-blog.csdnimg.cn/20200615221120928.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3p5eF9seQ==,size_16,color_FFFFFF,t_70
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[50. _ _]: https://leetcode-cn.com/problems/di-yi-ge-zhi-chu-xian-yi-ci-de-zi-fu-lcof/solution/mian-shi-ti-50-di-yi-ge-zhi-chu-xian-yi-ci-de-zi-3/
[50.java _99.9]: https://leetcode-cn.com/problems/di-yi-ge-zhi-chu-xian-yi-ci-de-zi-fu-lcof/solution/mian-shi-ti-50java-shi-yong-shu-zu-dai-ti-ha-xi-bi/
[Link 1]: https://leetcode-cn.com/problems/di-yi-ge-zhi-chu-xian-yi-ci-de-zi-fu-lcof/solution/yi-ge-jian-dan-gao-xiao-de-tong-ji-fang-fa-by-caix/