【剑指Offer】28、数组中出现次数超过一半的数字

 1 public static int MoreThanHalfNum_Solution(int [] array) {
 2         if (array.length == 0) {
 3             return 0;
 4         }
 5         //分别存放重复的元素以及出现的次数
 6         HashMap<Integer, Integer> map = new HashMap<>();
 7         int len = array.length;
 8         for (int i = 0; i < len; i++) {
 9             if (map.containsKey(array[i])) {
10                 Integer integer = map.get(array[i]);
11                 //++integer 此处必须这样写，因为需要先增再放
12                 map.put(array[i], ++integer);
13             } else {
14                 map.put(array[i], 1);
15             }
16         }
17         Iterator iter = map.entrySet().iterator();
18         while (iter.hasNext()) {
19             Map.Entry entry = (Map.Entry) iter.next();
20             Integer key = (Integer) entry.getKey();
21             Integer val = (Integer) entry.getValue();
22             if (val > array.length / 2) {
23                 return key;
24             }
25         }
26         return 0;
27     }

 1 public static int MoreThanHalfNum_Solution01(int [] array) {
 2         Arrays.sort(array);
 3         int count=0;
 4         //数组排序后，如果符合条件的数存在，则一定是数组中间那个数
 5         for(int i=0;i<array.length;i++){
 6             if(array[i]==array[array.length/2]){
 7                 count++;
 8             }
 9         }
10         if(count>array.length/2){
11             return array[array.length/2];
12         }else{
13             return 0;
14         }
15     }

1 public static void main(String[] args) {
2         int[] array={1,2,3,2,2,2,5,4,2};
3         int value = MoreThanHalfNum_Solution(array);
4         System.out.println(value);
5     }
6 输出:2