/*
* Copyright (C) 2006 The Android Open Source Project
*
* 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.taobao.utils;
/**
* SparseIntArrays map integers to integers. Unlike a normal array of integers,
* there can be gaps in the indices. It is intended to be more memory efficient
* than using a HashMap to map Integers to Integers, both because it avoids
* auto-boxing keys and values and its data structure doesn't rely on an extra entry object
* for each mapping.
*
* <p>Note that this container keeps its mappings in an array data structure,
* using a binary search to find keys. The implementation is not intended to be appropriate for
* data structures
* that may contain large numbers of items. It is generally slower than a traditional
* HashMap, since lookups require a binary search and adds and removes require inserting
* and deleting entries in the array. For containers holding up to hundreds of items,
* the performance difference is not significant, less than 50%.</p>
*
* <p>It is possible to iterate over the items in this container using
* {@link #keyAt(int)} and {@link #valueAt(int)}. Iterating over the keys using
* <code>keyAt(int)</code> with ascending values of the index will return the
* keys in ascending order, or the values corresponding to the keys in ascending
* order in the case of <code>valueAt(int)</code>.</p>
*/
public class SparseIntArray implements Cloneable {
private static final int[] EMPTY_INT_ARRAY = new int[0];
private int[] mKeys;
private int[] mValues;
private int mSize;
/**
* Creates a new SparseIntArray containing no mappings.
*/
public SparseIntArray() {
this(10);
}
/**
* Creates a new SparseIntArray containing no mappings that will not
* require any additional memory allocation to store the specified
* number of mappings. If you supply an initial capacity of 0, the
* sparse array will be initialized with a light-weight representation
* not requiring any additional array allocations.
*/
public SparseIntArray(int initialCapacity) {
if (initialCapacity == 0) {
mKeys = SparseIntArray.EMPTY_INT_ARRAY;
mValues = SparseIntArray.EMPTY_INT_ARRAY;
} else {
mKeys = new int[initialCapacity];
mValues = new int[mKeys.length];
}
mSize = 0;
}
/**
* Given the current size of an array, returns an ideal size to which the array should grow.
* This is typically double the given size, but should not be relied upon to do so in the
* future.
*/
public static int growSize(int currentSize) {
return currentSize <= 4 ? 8 : currentSize + (currentSize >> 1);
}
@Override
public SparseIntArray clone() {
SparseIntArray clone = null;
try {
clone = (SparseIntArray) super.clone();
clone.mKeys = mKeys.clone();
clone.mValues = mValues.clone();
} catch (CloneNotSupportedException cnse) {
/* ignore */
}
return clone;
}
/**
* Gets the int mapped from the specified key, or <code>0</code>
* if no such mapping has been made.
*/
public int get(int key) {
return get(key, 0);
}
/**
* Gets the int mapped from the specified key, or the specified value
* if no such mapping has been made.
*/
public int get(int key, int valueIfKeyNotFound) {
int i = binarySearch(mKeys, mSize, key);
if (i < 0) {
return valueIfKeyNotFound;
} else {
return mValues[i];
}
}
/**
* Removes the mapping from the specified key, if there was any.
*/
public void delete(int key) {
int i = binarySearch(mKeys, mSize, key);
if (i >= 0) {
removeAt(i);
}
}
/**
* Removes the mapping at the given index.
*/
public void removeAt(int index) {
System.arraycopy(mKeys, index + 1, mKeys, index, mSize - (index + 1));
System.arraycopy(mValues, index + 1, mValues, index, mSize - (index + 1));
--mSize;
}
/**
* Adds a mapping from the specified key to the specified value,
* replacing the previous mapping from the specified key if there
* was one.
*/
public void put(int key, int value) {
int i = binarySearch(mKeys, mSize, key);
if (i >= 0) {
mValues[i] = value;
} else {
i = ~i;
mKeys = insertElementIntoIntArray(mKeys, mSize, i, key);
mValues = insertElementIntoIntArray(mValues, mSize, i, value);
++mSize;
}
}
/**
* Returns the number of key-value mappings that this SparseIntArray
* currently stores.
*/
public int size() {
return mSize;
}
/**
* Given an index in the range <code>0...size()-1</code>, returns
* the key from the <code>index</code>th key-value mapping that this
* SparseIntArray stores.
*
* <p>The keys corresponding to indices in ascending order are guaranteed to
* be in ascending order, e.g., <code>keyAt(0)</code> will return the
* smallest key and <code>keyAt(size()-1)</code> will return the largest
* key.</p>
*/
public int keyAt(int index) {
return mKeys[index];
}
/**
* Given an index in the range <code>0...size()-1</code>, returns
* the value from the <code>index</code>th key-value mapping that this
* SparseIntArray stores.
*
* <p>The values corresponding to indices in ascending order are guaranteed
* to be associated with keys in ascending order, e.g.,
* <code>valueAt(0)</code> will return the value associated with the
* smallest key and <code>valueAt(size()-1)</code> will return the value
* associated with the largest key.</p>
*/
public int valueAt(int index) {
return mValues[index];
}
/**
* Returns the index for which {@link #keyAt} would return the
* specified key, or a negative number if the specified
* key is not mapped.
*/
public int indexOfKey(int key) {
return binarySearch(mKeys, mSize, key);
}
/**
* Returns an index for which {@link #valueAt} would return the
* specified key, or a negative number if no keys map to the
* specified value.
* Beware that this is a linear search, unlike lookups by key,
* and that multiple keys can map to the same value and this will
* find only one of them.
*/
public int indexOfValue(int value) {
for (int i = 0; i < mSize; ++i) {
if (mValues[i] == value) {
return i;
}
}
return -1;
}
/**
* Removes all key-value mappings from this SparseIntArray.
*/
public void clear() {
mSize = 0;
}
/**
* Puts a key/value pair into the array, optimizing for the case where
* the key is greater than all existing keys in the array.
*/
public void append(int key, int value) {
if (mSize != 0 && key <= mKeys[mSize - 1]) {
put(key, value);
return;
}
mKeys = appendElementIntoIntArray(mKeys, mSize, key);
mValues = appendElementIntoIntArray(mValues, mSize, value);
mSize++;
}
private int binarySearch(int[] array, int size, int value) {
int lo = 0;
int hi = size - 1;
while (lo <= hi) {
int mid = (lo + hi) >>> 1;
int midVal = array[mid];
if (midVal < value) {
lo = mid + 1;
} else if (midVal > value) {
hi = mid - 1;
} else {
return mid; // value found
}
}
return ~lo; // value not present
}
private int[] appendElementIntoIntArray(int[] array, int currentSize, int element) {
if (currentSize > array.length) {
throw new IllegalArgumentException("Bad currentSize, originalSize: " + array.length + " currentSize: " + currentSize);
}
if (currentSize + 1 > array.length) {
int[] newArray = new int[SparseIntArray.growSize(currentSize)];
System.arraycopy(array, 0, newArray, 0, currentSize);
array = newArray;
}
array[currentSize] = element;
return array;
}
private int[] insertElementIntoIntArray(int[] array, int currentSize, int index, int element) {
if (currentSize > array.length) {
throw new IllegalArgumentException("Bad currentSize, originalSize: " + array.length + " currentSize: " + currentSize);
}
if (currentSize + 1 <= array.length) {
System.arraycopy(array, index, array, index + 1, currentSize - index);
array[index] = element;
return array;
}
int[] newArray = new int[SparseIntArray.growSize(currentSize)];
System.arraycopy(array, 0, newArray, 0, index);
newArray[index] = element;
System.arraycopy(array, index, newArray, index + 1, array.length - index);
return newArray;
}
/**
* {@inheritDoc}
*
* <p>This implementation composes a string by iterating over its mappings.
*/
@Override
public String toString() {
if (size() <= 0) {
return "{}";
}
StringBuilder buffer = new StringBuilder(mSize * 28);
buffer.append('{');
for (int i = 0; i < mSize; i++) {
if (i > 0) {
buffer.append(", ");
}
int key = keyAt(i);
buffer.append(key);
buffer.append('=');
int value = valueAt(i);
buffer.append(value);
}
buffer.append('}');
return buffer.toString();
}
}