fd

Author: dingjikerbo

solution/src/main/java/com/inuker/solution/TopKFrequentElements.java

@@ -15,35 +15,44 @@
 
 public class TopKFrequentElements {
 
-    // 耗时46ms，最差复杂度O(nlgn)
+    /**
+     * 先统计每个元素次数，再用Priority排序
+     */
+    // 耗时46ms，最差复杂度O(nlgn)，当k<<n时为O(n)
     public List<Integer> topKFrequent(int[] nums, int k) {
-        Map<Integer, Integer> map = new TreeMap<Integer, Integer>();
+        HashMap<Integer, Integer> map = new HashMap<>();
         for (int n : nums) {
             map.put(n, map.getOrDefault(n, 0) + 1);
         }
-        Queue<int[]> queue = new PriorityQueue<>(new Comparator<int[]>() {
+        Queue<Integer> queue = new PriorityQueue<Integer>(8, new Comparator<Integer>() {
             @Override
-            public int compare(int[] o1, int[] o2) {
-                return o2[1] - o1[1];
+            public int compare(Integer o1, Integer o2) {
+                return map.get(o1) - map.get(o2);
             }
         });
-        for (int key : map.keySet()) {
-            queue.add(new int[] { key, map.get(key) });
+        for (Integer n : map.keySet()) {
+            queue.offer(n);
+            if (queue.size() > k) {
+                queue.poll();
+            }
         }
-        List<Integer> list = new LinkedList<Integer>();
-        for (int i = 1; i <= k && !queue.isEmpty(); i++) {
-            list.add(queue.poll()[0]);
+        List<Integer> list = new LinkedList<>();
+        while (!queue.isEmpty()) {
+            list.add(queue.poll());
         }
         return list;
     }
 
-    // 耗时23ms，复杂度O(n)
+    // 耗时23ms，时间复杂度O(n)，空间复杂度O(n)
     public List<Integer> topKFrequent2(int[] nums, int k) {
         Map<Integer, Integer> map = new HashMap<Integer, Integer>();
+        int max = 0;
         for (int n : nums) {
-            map.put(n, map.getOrDefault(n, 0) + 1);
+            int count = map.getOrDefault(n, 0) + 1;
+            map.put(n, count);
+            max = Math.max(max, count);
         }
-        List<Integer>[] lists = new LinkedList[nums.length + 1];
+        List<Integer>[] lists = new LinkedList[max + 1];
         for (int key : map.keySet()) {
             int count = map.get(key);
             if (lists[count] == null) {

test/src/main/java/com/inuker/test/Test.java

@@ -0,0 +1,26 @@
+package com.inuker.test;
+
+/**
+ * Created by liwentian on 2017/12/4.
+ */
+
+public class Test {
+
+    Caller mCaller;
+
+     void call(String name) {
+        if (mCaller == null) {
+            mCaller = new Caller() {
+                @Override
+                public void call() {
+                    System.out.println(name);
+                }
+            };
+        }
+        mCaller.call();
+    }
+
+    interface Caller {
+        void call();
+    }
+}

test/src/main/java/com/inuker/test/main.java

@@ -1,5 +1,6 @@
 package com.inuker.test;
 
+import com.inuker.solution.NestedInteger;
 import com.leetcode.library.Interval;
 import com.leetcode.library.TreeNode;
 
@@ -16,34 +17,40 @@
 import java.util.List;
 import java.util.PriorityQueue;
 import java.util.Queue;
+import java.util.Random;
 import java.util.Set;
 import java.util.Stack;
+import java.util.TreeMap;
 
 public class main {
 
     public static void main(String[] args) {
-
+        Test test = new Test();
+        test.call("hello");
+        test.call("how");
     }
 
-    class Logger {
-
-        HashMap<String, Integer> map = new HashMap<>();
-
-        /** Initialize your data structure here. */
-        public Logger() {
-
+    public List<Integer> topKFrequent(int[] nums, int k) {
+        HashMap<Integer, Integer> map = new HashMap<>();
+        for (int n : nums) {
+            map.put(n, map.getOrDefault(n, 0) + 1);
         }
-
-        /** Returns true if the message should be printed in the given timestamp, otherwise returns false.
-         If this method returns false, the message will not be printed.
-         The timestamp is in seconds granularity. */
-        public boolean shouldPrintMessage(int timestamp, String message) {
-            int time = map.getOrDefault(message, -100);
-            if (time <= timestamp - 10) {
-                map.put(message, timestamp);
-                return true;
+        Queue<Integer> queue = new PriorityQueue<>(new Comparator<Integer>() {
+            @Override
+            public int compare(Integer o1, Integer o2) {
+                return map.get(o1) - map.get(o2);
+            }
+        });
+        for (Integer n : map.keySet()) {
+            queue.add(n);
+            if (queue.size() > k) {
+                queue.poll();
             }
-            return false;
         }
+        List<Integer> list = new LinkedList<>();
+        while (!queue.isEmpty()) {
+            list.add(queue.poll());
+        }
+        return list;
     }
 }