1 public static void main(String[] args) { 2         Scanner scanner = new Scanner(System.in); 3         String src =http://www.mamicode.com/ scanner.next(); 4         HashMap<Character,Integer> items = new HashMap<Character,Integer>(); 5         for(int i=0;i<src.length();i++){ 6             if(!items.containsKey(src.charAt(i))){ 7                 items.put(src.charAt(i), 1); 8             }else{ 9                 System.out.println(src.charAt(i));10                 break;11             }12         }13     }

 1 public class Main { 2  3     public static void main(String[] args) { 4         char[] array = {‘a‘,‘s‘,‘d‘,‘a‘,‘s‘}; 5      6         if (getFirstTwiceChar(array) != -1) { 7             System.out.println(array[getFirstTwiceChar(array)]); 8         } 9         10     }11     12     public static int getFirstTwiceChar(char[] array){13         14         if (array == null || array.length < 2) {15             return -1;16         }17         /* 一个整数数组，下标表示字符的大小*/18         int[] table = new int[256];19         20         for (int i = 0; i < array.length; i++) {21             22             if(table[array[i]] == 0){23                 /* 将首次出现的字符在数组中置1 */24                 table[array[i]] = 1;25             } else {26                 /* 字符第二次出现 */27                 return i;28             }29             30         }31         return -1;32     }33 }

 1 import java.util.ArrayList; 2 import java.util.Scanner; 3  4  5 public class Main { 6  7      8     public static void main(String[] args) { 9         10         Scanner input = new Scanner(System.in);11         ArrayList<String> strings = new ArrayList<>();12         13         while(input.hasNext()){14             strings.add(input.nextLine());15         }16         17         int[] counts = new int[strings.size()];18         /* 用于跟踪位置的变化 */19         int[] labels = new int[strings.size()];20         21         for (int i = 0; i < labels.length; i++) {22             labels[i] = i;23         }24         25         for (int i = 0; i < counts.length; i++) {26             counts[i] = countSubstr(strings.get(i), "your", true);27         }28         sort(counts, labels);29         for (int i = 0; i < labels.length; i++) {30             System.out.println(strings.get(labels[i]));31         }32     }33     /**34      * 冒泡排序35      * @param counts36      * @param labels37      */38     public static void sort(int[] counts, int[] labels){39         40         for(int i = counts.length-1; i > 0 ; i--){41             for(int j = 0; j < i; j++){42                 /* 从高到低 */43                 if (counts[j] < counts[j+1]) {44                     45                     int temp = counts[j];46                     counts[j] = counts[j+1];47                     counts[j+1] = temp;48                     49                     /* 跟踪位置的变化 */50                     int t = labels[j];51                     labels[j] = labels[j+1];52                     labels[j+1] = t;53                     54                 }55                 56             }57         }58     }59     60     public static int countSubstr(String src, String sub, boolean isIgnore) {  61         int count = 0, start = 0;  62         if (isIgnore) {  63             src =http://www.mamicode.com/ src.toLowerCase();  64             sub = sub.toLowerCase();  65         }  66         while ((start = src.indexOf(sub, start)) >= 0) {  67             start += sub.length();  68             count++;  69         }  70         return count;  71     }   72 }