LC#706 hashmap implementaion from scratch

Author: NirmalSilwal

Leetcode/easy/DesignHashMap706.java

@@ -0,0 +1,126 @@
+package easy;
+
+import java.util.LinkedList;
+
+public class DesignHashMap706 {
+
+	private class HTPair {
+		int key;
+		int value;
+
+		HTPair(int key, int value) {
+			this.key = key;
+			this.value = value;
+		}
+	}
+
+	private int size;
+	private static final int DEFAULT_CAPACITY = 10;
+	private LinkedList<HTPair>[] bucketarray;
+
+	/** Initialize your data structure here. */
+	public DesignHashMap706() {
+		initBucket(DEFAULT_CAPACITY);
+		size = 0;
+	}
+
+	private void initBucket(int N) {
+		bucketarray = new LinkedList[N];
+		for (int bi = 0; bi < bucketarray.length; bi++) {
+			bucketarray[bi] = new LinkedList<HTPair>();
+		}
+	}
+
+	/** value will always be non-negative. */
+	public void put(int key, int value) {
+		int bucketIndex = hashFunction(key);
+		int dataIndex = getDataWithinBucket(key, bucketIndex);
+
+		if (dataIndex == -1) {
+			// no index found
+			HTPair newPair = new HTPair(key, value);
+			bucketarray[bucketIndex].add(newPair);
+			size++;
+		} else {
+			LinkedList<HTPair> bucketLocation = bucketarray[bucketIndex];
+			bucketLocation.get(dataIndex).value = value;
+		}
+
+		// rehasing threshold
+		double lambda = size * 1.0 / bucketarray.length;
+		if (lambda > 2.0) {
+			rehash();
+		}
+	}
+
+	private void rehash() {
+		LinkedList<HTPair>[] oldbucket = bucketarray;
+		initBucket(oldbucket.length * 2);
+		size = 0;
+		for (int bi = 0; bi < oldbucket.length; bi++) {
+			for (HTPair pairs : oldbucket[bi]) {
+				put(pairs.key, pairs.value);
+			}
+		}
+	}
+
+	private int hashFunction(Integer key) {
+		int hashCode = key.hashCode();
+		return Math.abs(hashCode) % bucketarray.length;
+	}
+
+	private int getDataWithinBucket(int keys, int bi) {
+		int id = 0;
+		for (HTPair pairs : bucketarray[bi]) {
+			if (pairs.key == keys) // == here because we used int as key,value
+				return id;
+			id++;
+		}
+		return -1;
+	}
+
+	/**
+	 * Returns the value to which the specified key is mapped, or -1 if this map
+	 * contains no mapping for the key
+	 */
+	public int get(int key) {
+		int bucketIndex = hashFunction(key);
+		int dataIndex = getDataWithinBucket(key, bucketIndex);
+
+		if (dataIndex == -1) {
+			return dataIndex; // no index found
+		} else {
+			LinkedList<HTPair> bucketLocation = bucketarray[bucketIndex];
+			return bucketLocation.get(dataIndex).value;
+		}
+	}
+
+	/**
+	 * Removes the mapping of the specified value key if this map contains a
+	 * mapping for the key
+	 */
+	public void remove(int key) {
+		int bucketIndex = hashFunction(key);
+		int dataIndex = getDataWithinBucket(key, bucketIndex);
+
+		if (dataIndex == -1) {
+			return;
+		} else {
+			LinkedList<HTPair> bucketLocation = bucketarray[bucketIndex];
+			bucketLocation.remove(dataIndex);
+			size--;
+		}
+	}
+}
+
+/**
+ * Your MyHashMap object will be instantiated and called as such:
+ * 
+ * MyHashMap obj = new MyHashMap();
+ * 
+ * obj.put(key,value);
+ * 
+ * int param_2 = obj.get(key);
+ * 
+ * obj.remove(key);
+ */