找出字符串中第一个只出现一次的字符

以你之姓@ 2023-07-01 08:32 1阅读 0赞

[https://www.nowcoder.com/practice/e896d0f82f1246a3aa7b232ce38029d4?tpId=37&tqId=21282&tPage=3&rp=&ru=%2Fta%2Fhuawei&qru=%2Fta%2Fhuawei%2Fquestion-ranking][https_www.nowcoder.com_practice_e896d0f82f1246a3aa7b232ce38029d4_tpId_37_tqId_21282_tPage_3_rp_ru_2Fta_2Fhuawei_qru_2Fta_2Fhuawei_2Fquestion-ranking]

## 一、题目描述 ##

找出字符串中第一个只出现一次的字符

## 二、代码实现 ##

使用哈希表：

import java.util.Scanner;
    import java.util.Map;
    import java.util.LinkedHashMap;
    
    public class Main {
        public static void main(String[] args) {
            Scanner sc = new Scanner(System.in);
            
            while (sc.hasNextLine()) {
                String input = sc.nextLine();
                LinkedHashMap<Character, Integer> map = new LinkedHashMap<>();
                
                for (int i=0; i<input.length(); i++) {
                    char ch = input.charAt(i);
                    if (map.get(ch) == null) {
                        map.put(ch, 1);
                    } else {
                        map.put(ch, map.get(ch)+1);
                    }
                }
                
                char ch = ' ';
                for (Map.Entry<Character, Integer> entry : map.entrySet()) {
                    if (entry.getValue() == 1) {
                        //System.out.println(entry.getKey());
                    	ch = entry.getKey();
                        break;
                    }
                }
                if (ch == ' ') {
                	System.out.println(-1);
                } else {
                	System.out.println(ch);
                }
                
            }
        }
    }

暴力法（O(N^2)）：

import java.util.Scanner;
    public class Main {
        
        public static void main(String[] args) {
            Scanner sc = new Scanner(System.in);
            
            while (sc.hasNextLine()) {
                String input = sc.nextLine();
                
                boolean flag = true;
                for (int i=0; i<input.length(); i++) {
                    char ch = input.charAt(i);
                    if (input.indexOf(ch) == input.lastIndexOf(ch)) {
                        System.out.println(ch);
                        flag = false;
                        break;
                    }
                }
                
                if (flag) {
                    System.out.println(-1);
                }
            }
        }
    }

[https_www.nowcoder.com_practice_e896d0f82f1246a3aa7b232ce38029d4_tpId_37_tqId_21282_tPage_3_rp_ru_2Fta_2Fhuawei_qru_2Fta_2Fhuawei_2Fquestion-ranking]: https://www.nowcoder.com/practice/e896d0f82f1246a3aa7b232ce38029d4?tpId=37&tqId=21282&tPage=3&rp=&ru=%2Fta%2Fhuawei&qru=%2Fta%2Fhuawei%2Fquestion-ranking