feat[treemap]: fast read only tree map

net/src/main/java/com/zfoo/net/util/ReadOnlyTreeMapIntLong.java

@@ -0,0 +1,127 @@
+/*
+ * Copyright (C) 2020 The zfoo Authors
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
+ * in compliance with the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software distributed under the License is distributed
+ * on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and limitations under the License.
+ */
+
+package com.zfoo.net.util;
+
+import com.zfoo.protocol.collection.ArrayUtils;
+
+import java.util.NoSuchElementException;
+import java.util.Objects;
+import java.util.TreeMap;
+
+/**
+ * @author godotg
+ */
+public class ReadOnlyTreeMapIntLong {
+
+    private int[] keys;
+    private long[] values;
+
+    public ReadOnlyTreeMapIntLong(TreeMap<Integer, Long> treeMap) {
+        var size = treeMap.size();
+        keys = new int[size];
+        values = new long[size];
+
+        // TreeMap遍历是有序的，直接放入数组中就能直接得到从小到大的有序数组
+        var index = 0;
+        for (var entry : treeMap.entrySet()) {
+            var key = entry.getKey();
+            var value = entry.getValue();
+            keys[index] = key;
+            values[index] = value;
+            index++;
+        }
+    }
+
+    public boolean contains(int key) {
+        return indexOf(key) >= 0;
+    }
+
+    public long get(int key) {
+        var index = indexOf(key);
+        if (index < 0) {
+            throw new NoSuchElementException();
+        }
+        return values[index];
+    }
+
+    public long getByIndex(int index) {
+        Objects.checkIndex(index, values.length);
+        return values[index];
+    }
+
+    public int indexOf(int key) {
+        var low = 0;
+        var high = keys.length - 1;
+        while (low <= high) {
+            int mid = (low + high) / 2;
+            if (keys[mid] == key) {
+                return mid;
+            } else if (keys[mid] < key) {
+                low = mid + 1;
+            } else {
+                high = mid - 1;
+            }
+        }
+        return -1;
+    }
+
+    public int indexOfCeilingKey(int key) {
+        if (ArrayUtils.isEmpty(keys)) {
+            return -1;
+        }
+
+        var size = keys.length;
+        // 目标数小于或等于数组的第一个元素
+        if (key <= keys[0]) {
+            return 0;
+        }
+        // 目标数大于数组的第一个元素
+        if (key > keys[size - 1]) {
+            return 0;
+        }
+
+        // 二分查找目标数
+        var low = 0;
+        var high = size - 1;
+        var nearestIndex = -1;
+
+        while (low <= high) {
+            var mid = low + (high - low) / 2;
+            if (keys[mid] == key) {
+                nearestIndex = mid;
+                break;
+            } else if (keys[mid] < key) {
+                low = mid + 1;
+            } else {
+                high = mid - 1;
+                nearestIndex = mid;
+            }
+        }
+
+        // 如果找到了目标数，那么它的邻近最大值就是目标数本身
+        if (nearestIndex == -1) {
+            return 0;
+        }
+
+        return nearestIndex;
+    }
+
+    public long getValueByCeilingKey(int key) {
+        var index = indexOfCeilingKey(key);
+        if (index < 0) {
+            throw new NoSuchElementException();
+        }
+        return values[index];
+    }
+
+}

net/src/test/java/com/zfoo/net/util/ReadOnlyTreeMapIntLongTest.java

@@ -0,0 +1,52 @@
+/*
+ * Copyright (C) 2020 The zfoo Authors
+ * Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except
+ * in compliance with the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software distributed under the License is distributed
+ * on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and limitations under the License.
+ */
+
+package com.zfoo.net.util;
+
+import org.junit.Assert;
+import org.junit.Test;
+
+import java.util.TreeMap;
+
+/**
+ * @author godotg
+ */
+public class ReadOnlyTreeMapIntLongTest {
+
+    @Test
+    public void test() {
+        var treeMap = new TreeMap<Integer, Long>();
+        for (var i = 0; i < 100; i = i + 2) {
+            treeMap.put(i, (long) i);
+        }
+
+        var fastTreeMap = new ReadOnlyTreeMapIntLong(treeMap);
+        Assert.assertEquals(fastTreeMap.get(0), 0);
+        Assert.assertEquals(fastTreeMap.get(8), 8);
+        Assert.assertEquals(fastTreeMap.get(98), 98);
+        Assert.assertFalse(fastTreeMap.contains(-1));
+        Assert.assertFalse(fastTreeMap.contains(1));
+        Assert.assertFalse(fastTreeMap.contains(100));
+        Assert.assertTrue(fastTreeMap.contains(44));
+        Assert.assertEquals(fastTreeMap.getValueByCeilingKey(-1), 0);
+        Assert.assertEquals(fastTreeMap.getValueByCeilingKey(-100), 0);
+        Assert.assertEquals(fastTreeMap.getValueByCeilingKey(0), 0);
+        Assert.assertEquals(fastTreeMap.getValueByCeilingKey(1), 2);
+        Assert.assertEquals(fastTreeMap.getValueByCeilingKey(45), 46);
+        Assert.assertEquals(fastTreeMap.getValueByCeilingKey(97), 98);
+        Assert.assertEquals(fastTreeMap.getValueByCeilingKey(100), 0);
+        Assert.assertEquals(fastTreeMap.indexOfCeilingKey(-1), 0);
+        Assert.assertEquals(fastTreeMap.indexOfCeilingKey(0), 0);
+        Assert.assertEquals(fastTreeMap.indexOfCeilingKey(1), 1);
+    }
+
+}