303. Range Sum Query - Immutable commit.

09-Segment-Tree/303-Range-Sum-Query-Immutable/src/Merger.java

@@ -0,0 +1,8 @@
+/**
+ * @Auther: lss
+ * @Date: 2019/2/27 20:53
+ * @Description:
+ */
+public interface Merger<E> {
+ E merge(E a, E b);
+}

09-Segment-Tree/303-Range-Sum-Query-Immutable/src/NumArray.java

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+/**
+ * @Auther: lss
+ * @Date: 2019/3/5 16:58
+ * @Description:
+ */
+public class NumArray {
+
+ private SegmentTree<Integer> segmentTree;
+
+ public NumArray(int[] nums) {
+ if (nums.length > 0) {
+ Integer[] data = new Integer[nums.length];
+ for (int i = 0; i < nums.length; i++)
+ data[i] = nums[i];
+ segmentTree = new SegmentTree<>(data, (a, b) -> a + b);
+ }
+ }
+
+ public int sumRange(int i, int j) {
+ if (segmentTree == null)
+ throw new IllegalArgumentException("Segment Tree is null");
+
+ return segmentTree.query(i, j);
+ }
+}

09-Segment-Tree/303-Range-Sum-Query-Immutable/src/SegmentTree.java

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+/**
+ * @Auther: lss
+ * @Date: 2019/2/26 20:53
+ * @Description:
+ */
+public class SegmentTree<E> {
+
+ private E[] tree;
+ private E[] data;
+ private Merger<E> merger;
+
+ public SegmentTree(E[] arr, Merger<E> merger) {
+
+ this.merger = merger;
+
+ data = (E[]) new Object[arr.length];
+ for (int i = 0; i < arr.length; i++)
+ data[i] = arr[i];
+
+ tree = (E[]) new Object[4 * arr.length];
+ buildSegmentTree(0, 0, data.length - 1);
+ }
+
+ // 在treeIndex的位置创建表示区间[l...r]的线段树
+ private void buildSegmentTree(int treeIndex, int l, int r) {
+
+ if (l == r) {
+ tree[treeIndex] = data[l];
+ return;
+ }
+
+ int leftTreeIndex = leftChild(treeIndex);
+ int rightTreeIndex = rightChild(treeIndex);
+ // l+r 可能会溢出 所以采用这种
+ int mid = l + (r - l) / 2;
+ buildSegmentTree(leftTreeIndex, l, mid);
+ buildSegmentTree(rightTreeIndex, mid + 1, r);
+
+ tree[treeIndex] = merger.merge(tree[leftTreeIndex], tree[rightTreeIndex]);
+
+ }
+
+ public int getSize() {
+ return data.length;
+ }
+
+ public E get(int index) {
+ if (index < 0 || index >= data.length)
+ throw new IllegalArgumentException("Index in illegal");
+ return data[index];
+ }
+
+ // 返回完全二叉树的数组表示中，一个索引所表示的元素的左孩子节点的索引
+ private int leftChild(int index) {
+ return 2 * index + 1;
+ }
+
+ // 返回完全二叉树的数组表示中，一个索引所表示的元素的右孩子节点的索引
+ private int rightChild(int index) {
+ return 2 * index + 2;
+ }
+
+ // 返回区间[queryL,queryR]的值
+ public E query(int queryL, int queryR) {
+
+ if (queryL < 0 || queryL >= data.length ||
+ queryR < 0 || queryR >= data.length || queryL > queryR)
+ throw new IllegalArgumentException("Index is illegal.");
+
+ return query(0, 0, data.length - 1, queryL, queryR);
+ }
+
+ // 在以treeId为根的线段树中[l...r]的范围里，搜索区间[queryL...queryR]的值
+ private E query(int treeIndex, int l, int r, int queryL, int queryR) {
+
+ if (l == queryL && r == queryR)
+ return tree[treeIndex];
+
+ int mid = l + (r - l) / 2;
+ int leftTreeIndex = leftChild(treeIndex);
+ int rightTreeIndex = rightChild(treeIndex);
+
+ if (queryL >= mid + 1)
+ return query(rightTreeIndex, mid + 1, r, queryL, queryR);
+ else if (queryR <= mid)
+ return query(leftTreeIndex, l, mid, queryL, queryR);
+
+ E leftResult = query(leftTreeIndex, l, mid, queryL, mid);
+ E rightResult = query(rightTreeIndex, mid + 1, r, mid + 1, queryR);
+ return merger.merge(leftResult, rightResult);
+ }
+
+ @Override
+ public String toString() {
+ StringBuilder res = new StringBuilder();
+ res.append('[');
+ for (int i = 0; i < tree.length; i++) {
+ if (tree[i] != null)
+ res.append(tree[i]);
+ else
+ res.append("null");
+
+ if (i != tree.length - 1)
+ res.append(", ");
+ }
+ res.append(']');
+ return res.toString();
+ }
+
+}