Segment tree java implementation [closed]

Question

Do you know a good implementation of a (binary) segment tree in Java?

Withershins

Similar post: IntervalTree Java Implementation. – Sedgemoor

Here is an my implementation which is open source that does range min/max/sum query and also does interval stabbing queries. github.com/phishman3579/java-algorithms-implementation/blob/… – Kaunas

Answer 1

This has been implemented within the open source Layout Management SW Package project

Here is a link to the sub package

You might find the code useful. I have neither verified it nor run it and I cannot find the license the code is provided under from a quick search of the code and website so Caveat Emptor.

You may be able to contact the authors but the last activity appears to have been August 2008.

Manana

License info here: code.google.com/p/layout-managment-sw-package – Morley

Answer 2

public class SegmentTree {
    public static class STNode {
        int leftIndex;
        int rightIndex;
        int sum;
        STNode leftNode;
        STNode rightNode;
    }

    static STNode constructSegmentTree(int[] A, int l, int r) {
        if (l == r) {
            STNode node = new STNode();
            node.leftIndex = l;
            node.rightIndex = r;
            node.sum = A[l];
            return node;
        }
        int mid = (l + r) / 2;
        STNode leftNode = constructSegmentTree(A, l, mid);
        STNode rightNode = constructSegmentTree(A, mid+1, r);
        STNode root = new STNode();
        root.leftIndex = leftNode.leftIndex;
        root.rightIndex = rightNode.rightIndex;
        root.sum = leftNode.sum + rightNode.sum;
        root.leftNode = leftNode;
        root.rightNode = rightNode;
        return root;
    }

    static int getSum(STNode root, int l, int r) {
        if (root.leftIndex >= l && root.rightIndex <= r) {
            return root.sum;
        }
        if (root.rightIndex < l || root.leftIndex > r) {
            return 0;
        }
        return getSum(root.leftNode, l, r) + getSum(root.rightNode, l, r);
    }

    /**
     * 
     * @param root
     * @param index index of number to be updated in original array 
     * @param newValue
     * @return difference between new and old values
     */
    static int updateValueAtIndex(STNode root, int index, int newValue) {
        int diff = 0;
        if(root.leftIndex==root.rightIndex && index == root.leftIndex) {
            // We actually reached to the leaf node to be updated
            diff = newValue-root.sum;
            root.sum=newValue;
            return diff;
        }
        int mid = (root.leftIndex + root.rightIndex) / 2;
        if (index <= mid) {
            diff= updateValueAtIndex(root.leftNode, index, newValue);
        } else {
            diff= updateValueAtIndex(root.rightNode, index, newValue);
        }
        root.sum+=diff;
        return diff;
    }
}

Interpose

' STNode rightNode = constructSegmentTree(A, mid, r);' Should use 'mid+1' only then its working. – Disillusionize

Answer 3

Here it is:

import java.util.Scanner;

public class MinimumSegmentTree {

    static Scanner in = new Scanner(System.in);

    public static void main(String[] args) {
        final int n = in.nextInt();
        int[] a = new int[n];

        for (int i = 0; i < n; i++) {
            a[i] = in.nextInt();
        }

        int sizeOfSegmentTree = (int) Math.pow(2, Math.ceil(Math.log10(n) / Math.log10(2)));
        sizeOfSegmentTree = 2*sizeOfSegmentTree-1;

//      System.out.println(sizeOfSegmentTree);

        int[] segmentTree = new int[sizeOfSegmentTree];
        formSegmentTree(a, segmentTree, 0, n-1, 0);

//      for(int i=0; i<sizeOfSegmentTree; i++){
//          System.out.print(segmentTree[i]+" ");
//      }
//      System.out.println();

        final int q = in.nextInt();
        for (int i = 0; i < q; i++) {
            int s, e;
            s = in.nextInt();
            e = in.nextInt();

            int minOverRange = getMinimumOverRange(segmentTree, s, e, 0, n-1, 0);
            System.out.println(minOverRange);
        }
    }

    private static int getMinimumOverRange(int[] segmentTree, int qs, int qe, int s, int e, int pos) {
        if (qs <= s && qe >= e) {
            return segmentTree[pos];
        }
        if (qs > e || s > qe) {
            return 10000000;
        }

        int mid = (s + e) / 2;
        return Math.min(getMinimumOverRange(segmentTree, qs, qe, s, mid, 2 * pos + 1),
                getMinimumOverRange(segmentTree, qs, qe, mid+1, e, 2 * pos + 2));
    }

    private static void formSegmentTree(int[] a, int[] segmentTree, int s, int e, int pos) {
        if (e - s == 0) {
            segmentTree[pos] = a[s];
            return;

        }

        int mid = (s + e) / 2;

        formSegmentTree(a, segmentTree, s, mid, 2 * pos + 1);
        formSegmentTree(a, segmentTree, mid+1, e, 2 * pos + 2);

        segmentTree[pos] = Math.min(segmentTree[2 * pos + 1], segmentTree[2 * pos + 2]);

    }

}

Billionaire

Answer 4

Algo and unit tests:

public class NumArrayTest {

        @Test
        public void testUpdateSumRange_WithEmpty() throws Exception {
            NumArray numArray = new NumArray(new int[]{});
            assertEquals(0, numArray.sumRange(0, 0));
        }

        @Test
        public void testUpdateSumRange_WithSingleton() throws Exception {
            NumArray numArray = new NumArray(new int[]{1});
            assertEquals(1, numArray.sumRange(0, 0));
            numArray.update(0, 2);
            assertEquals(2, numArray.sumRange(0, 0));
        }

        @Test
        public void testUpdateSumRange_WithPairElements() throws Exception {
            NumArray numArray = new NumArray(new int[]{1,2,3,4,5,6});
            assertEquals(12, numArray.sumRange(2, 4));
            numArray.update(3, 2);
            assertEquals(10, numArray.sumRange(2, 4));
        }

        @Test
        public void testUpdateSumRange_WithInPairElements() throws Exception {
            NumArray numArray = new NumArray(new int[]{1,2,3,4,5,6,7});
            assertEquals(12, numArray.sumRange(2, 4));
            numArray.update(3, 2);
            assertEquals(10, numArray.sumRange(2, 4));
        }
    }



public class NumArray {

    private final Node root;

    private static class Node {
        private final int begin;
        private final int end;
        private final Node left;
        private final Node right;
        private int sum;

        public Node(int begin, int end, int sum, Node left, Node right) {
            this.begin = begin;
            this.end = end;
            this.sum = sum;
            this.left = left;
            this.right = right;
        }

        public boolean isSingle() {
            return begin == end;
        }

        public boolean contains(int i) {
            return i >= begin && i <= end;
        }

        public boolean inside(int i, int j) {
            return i <= begin && j >= end;
        }

        public boolean outside(int i, int j) {
            return i > end || j < begin;
        }

        public void setSum(int sum) {
            this.sum = sum;
        }
    }

    public NumArray(int[] nums) {
        if (nums.length == 0) {
            root = null;
        } else {
            root = buildNode(nums, 0, nums.length - 1);
        }
    }

    private Node buildNode(int[] nums, int begin, int end) {
        if (begin == end) {
            return new Node(begin, end, nums[begin], null, null);
        } else {
            int mid = (begin + end) / 2 + 1;
            Node left = buildNode(nums, begin, mid - 1);
            Node right = buildNode(nums, mid, end);
            return new Node(begin, end, left.sum + right.sum, left, right);
        }
    }

    public void update(int i, int val) {
        if (root == null) {
            return;
        }
        if (!root.contains(i)) {
            throw new IllegalArgumentException("i not in range");
        }
        update(root, i, val);
    }

    private int update(Node node, int i, int val) {
        if (node.isSingle()) {
            node.setSum(val);
        } else {
            Node nodeToUpdate = node.left.contains(i) ? node.left : node.right;
            int withoutNode = node.sum - nodeToUpdate.sum;
            node.setSum(withoutNode + update(nodeToUpdate, i, val));
        }
        return node.sum;
    }

    public int sumRange(int i, int j) {
        if (root == null) {
            return 0;
        }
        return sumRange(root, i, j);
    }

    private int sumRange(Node node, int i, int j) {
        if (node.outside(i, j)) {
            return 0;
        } else if (node.inside(i, j)) {
            return node.sum;
        } else {
            return sumRange(node.left, i, j) + sumRange(node.right, i, j);
        }
    }

}

Lamia