Create TheRocket.md

Author: Jerring

2018.12.14-leetcode347/TheRocket.md

@@ -0,0 +1,29 @@
+```java
+class Solution {
+    public List<Integer> topKFrequent(int[] nums, int k) {
+        // 构造一个从整数到出现次数的映射
+        Map<Integer, Integer> map = new HashMap<>();
+        for (int num : nums) {
+            map.put(num, map.getOrDefault(num, 0) + 1);
+        }
+        // 构造一个桶，桶内存放数据，桶的下标表示该数的出现次数
+        List<Integer>[] buckets = new ArrayList[nums.length + 1];
+        for (Map.Entry<Integer, Integer> entry : map.entrySet()) {
+            int num = entry.getKey();
+            int count = entry.getValue();
+            if (buckets[count] == null) {
+                buckets[count] = new ArrayList<>();
+            }
+            buckets[count].add(num);
+        }
+        List<Integer> topK = new ArrayList<>(k);
+        // 从后往前遍历桶，即从出现次数高的到出现次数低的，注意跳过不存在的桶
+        for (int i = buckets.length - 1; i >= 0 && topK.size() < k; --i) {
+            if (buckets[i] != null) {
+                topK.addAll(buckets[i]);
+            }
+        }
+        return topK;
+    }
+}
+```