Implementación java segmento de árbol

Question

¿Conoces una buena implementación de un (binario) segment tree en Java?

Answer 1

Esto se ha implementado dentro del código abierto Layout Management SW Package project

Aquí es una link to the sub package

Es posible encontrar el código útil. No lo he verificado ni lo he ejecutado y no puedo encontrar la licencia bajo la cual se proporciona el código de una búsqueda rápida del código y el sitio web, así que Caveat Emptor.

Es posible que pueda ponerse en contacto con los autores, pero la última actividad parece haber sido agosto de 2008.

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; 
    } 
} 

Answer 3

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); 
     } 
    } 

} 

Answer 4

Aquí está:

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]); 

    } 

}