My first submission

calculate_average_JurenIvan.sh

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+#!/bin/sh
+#
+#  Copyright 2023 The original 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.
+#
+
+JAVA_OPTS="--enable-preview"
+java $JAVA_OPTS --class-path target/average-1.0.0-SNAPSHOT.jar dev.morling.onebrc.CalculateAverage_JurenIvan

src/main/java/dev/morling/onebrc/CalculateAverage_JurenIvan.java

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+/*
+ *  Copyright 2023 The original 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 dev.morling.onebrc;
+
+import java.io.IOException;
+import java.io.RandomAccessFile;
+import java.nio.channels.FileChannel;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.util.Arrays;
+import java.util.Objects;
+import java.util.TreeMap;
+import java.util.stream.Collectors;
+import java.util.stream.IntStream;
+
+import static java.lang.Math.round;
+import static java.nio.channels.FileChannel.MapMode.READ_ONLY;
+import static java.nio.file.StandardOpenOption.READ;
+
+public class CalculateAverage_JurenIvan {
+
+    private static final String FILE_NAME = "./measurements.txt";
+
+    public static void main(String[] args) throws IOException {
+        long[] segments = getSegments(Runtime.getRuntime().availableProcessors());
+
+        var result = IntStream.range(0, segments.length - 1)
+                .parallel()
+                .mapToObj(i -> processSegment(segments[i], segments[i + 1]))
+                .flatMap(m -> Arrays.stream(m.hashTable).filter(Objects::nonNull))
+                .collect(Collectors.toMap(m -> new String(m.city), m -> m, Measurement::merge, TreeMap::new));
+
+        System.out.println(result);
+    }
+
+    private static LinearProbingHashMap processSegment(long start, long end) {
+        var results = new LinearProbingHashMap(1 << 19);
+
+        try (var fileChannel = (FileChannel) Files.newByteChannel(Path.of(FILE_NAME), READ)) {
+            var bb = fileChannel.map(READ_ONLY, start, end - start);
+            var buffer = new byte[100];
+
+            int limit = bb.limit();
+            for (int startLine = bb.position(); startLine < limit; startLine = bb.position()) {
+                int currentPosition = startLine;
+
+                byte b;
+                int hash = 7;
+                int wordLen = 0;
+                while (currentPosition < end && (b = bb.get(currentPosition++)) != ';') {
+                    buffer[wordLen++] = b;
+                    hash = hash * 31 + b;
+                }
+
+                int temp;
+                int negative = 1;
+                if (bb.get(currentPosition) == '-') {
+                    negative = -1;
+                    currentPosition++;
+                }
+
+                if (bb.get(currentPosition + 1) == '.') {
+                    temp = negative * ((bb.get(currentPosition) - '0') * 10 + (bb.get(currentPosition + 2) - '0'));
+                    currentPosition += 3;
+                }
+                else {
+                    temp = negative * ((bb.get(currentPosition) - '0') * 100 + ((bb.get(currentPosition + 1) - '0') * 10 + (bb.get(currentPosition + 3) - '0')));
+                    currentPosition += 4;
+                }
+
+                currentPosition++;
+
+                results.put(hash, buffer, wordLen, temp);
+
+                bb.position(currentPosition);
+            }
+        }
+        catch (IOException e) {
+            throw new RuntimeException(e);
+        }
+        return results;
+    }
+
+    private static long[] getSegments(int segmentCount) throws IOException {
+        try (var raf = new RandomAccessFile(FILE_NAME, "r")) {
+            long fileSize = raf.length();
+
+            if (fileSize < 100000) {
+                long[] chunks = new long[2];
+                chunks[1] = fileSize;
+                return chunks;
+            }
+
+            while (fileSize / segmentCount >= (Integer.MAX_VALUE - 150)) {
+                segmentCount *= 2;
+            }
+
+            long[] chunks = new long[segmentCount + 1];
+
+            chunks[0] = 0;
+            long segmentSize = fileSize / segmentCount;
+
+            for (int i = 1; i < segmentCount; i++) {
+                long chunkOffset = chunks[i - 1] + segmentSize;
+                raf.seek(chunkOffset);
+                while (raf.readByte() != '\n') {
+                }
+                chunks[i] = raf.getFilePointer();
+            }
+            chunks[segmentCount] = fileSize;
+            return chunks;
+        }
+    }
+
+    public static class LinearProbingHashMap {
+        final Measurement[] hashTable;
+        int slots;
+
+        public LinearProbingHashMap(int slots) {
+            this.slots = slots;
+            this.hashTable = new Measurement[slots];
+        }
+
+        void put(int hash, byte[] key, int len, int temperature) {
+            hash = Math.abs(hash);
+            int index = hash & (slots - 1);
+
+            int i = index;
+            while (hashTable[i] != null) {
+                if (keyIsEqual(key, hashTable[i].city, len)) { // handling hash collisions
+                    hashTable[i].add(temperature);
+                    return;
+                }
+                i++;
+                if (i == slots) {
+                    i = 0;
+                }
+            }
+
+            var cityArr = new byte[len];
+            System.arraycopy(key, 0, cityArr, 0, len);
+            hashTable[i] = new Measurement(cityArr, hash, temperature, temperature, 1, temperature);
+        }
+
+        private boolean keyIsEqual(byte[] one, byte[] other, int len) {
+            if (len != other.length)
+                return false;
+            for (int i = 0; i < len; i++) {
+                if (one[i] != other[i]) {
+                    return false;
+                }
+            }
+            return true;
+        }
+
+    }
+
+    static class Measurement {
+        byte[] city;
+        int hash;
+        int min;
+        int max;
+        int count;
+        long sum;
+
+        public Measurement(byte[] city, int hash, int min, int max, int count, long sum) {
+            this.city = city;
+            this.hash = hash;
+            this.min = min;
+            this.max = max;
+            this.count = count;
+            this.sum = sum;
+        }
+
+        public void add(int temperature) {
+            min = Math.min(min, temperature);
+            max = Math.max(max, temperature);
+            count++;
+            sum += temperature;
+        }
+
+        public Measurement merge(Measurement other) {
+            min = Math.min(min, other.min);
+            max = Math.max(max, other.max);
+            count += other.count;
+            sum += other.sum;
+            return this;
+        }
+
+        @Override
+        public String toString() {
+            return (min * 1.0) / 10 + "/" + round((sum * 1.0) / count) / 10.0 + "/" + (max * 1.0) / 10;
+        }
+
+        @Override
+        public int hashCode() {
+            return hash;
+        }
+
+        @Override
+        public boolean equals(Object obj) {
+            return Arrays.equals(city, ((Measurement) obj).city);
+        }
+    }
+}