/****************************************************************************** * * A segment tree data structure. * ******************************************************************************/ import java.util.Arrays; /** * The {@code SegmentTree} class is a structure for efficient search of cumulative data. * It performs Range Min, Max, Sum and Multiplication Queries in O(log(n)) time. *

* Also it has been develop with {@code LazyPropagation} for range updates, which means * when you perform update operations over a range, the update process affects the least nodes as possible * so that the bigger the range you want to update the less time it consumes to update it. Eventually those changes will be propagated * to the children and the whole array will be up to date. *

* Example: *

* SegmentTreeHeap st = new SegmentTreeHeap(new Integer[]{1,3,4,2,1, -2, 4}); * st.update(0,3, 1) * In the above case only the node that represents the range [0,3] will be updated (and not their children) so in this case * the update task will be less than n*log(n) *

* Memory usage: O(n) * * @author Ricardo Pacheco (base code) * @author Diogo Cordeiro (implemented range max and multiplication queries, plus other minor changes) * @link https://algs4.cs.princeton.edu/99misc/SegmentTree.java.html */ public class SegmentTree { private final STNode[] heap; private final int[] array; /** * Time-Complexity: O(n*log(n)) * * @param array the Initialization array */ public SegmentTree(int[] array) { this.array = Arrays.copyOf(array, array.length); // The max size of this array is about 2 * 2 ^ log2(n) + 1 int size = (int) (2 * Math.pow(2.0, Math.floor((Math.log(array.length) / Math.log(2.0)) + 1))); heap = new STNode[size]; build(1, 0, array.length); } public int size() { return array.length; } // Initialize the Nodes of the Segment tree private void build(int v, int from, int size) { heap[v] = new STNode(); heap[v].from = from; heap[v].to = from + size - 1; if (size == 1) { heap[v].sum = array[from]; heap[v].mul = array[from]; heap[v].min = array[from]; heap[v].max = array[from]; } else { // Build childs build(2 * v, from, size / 2); build(2 * v + 1, from + size / 2, size - size / 2); heap[v].sum = heap[2 * v].sum + heap[2 * v + 1].sum; heap[v].mul = heap[2 * v].mul * heap[2 * v + 1].mul; // min = min of the children heap[v].min = Math.min(heap[2 * v].min, heap[2 * v + 1].min); // max = max of the children heap[v].max = Math.max(heap[2 * v].max, heap[2 * v + 1].max); } } /** * Range Sum Query *

* Time-Complexity: O(log(n)) * * @param from from index * @param to to index * @return sum */ public int rsq(int from, int to) { return rsq(1, from, to); } private int rsq(int v, int from, int to) { STNode n = heap[v]; // If you did a range update that contained this node, you can infer the Sum without going down the tree if (n.pendingVal != null && contains(n.from, n.to, from, to)) { return (to - from + 1) * n.pendingVal; } if (contains(from, to, n.from, n.to)) { return heap[v].sum; } if (intersects(from, to, n.from, n.to)) { propagate(v); int leftSum = rsq(2 * v, from, to); int rightSum = rsq(2 * v + 1, from, to); return leftSum + rightSum; } return 0; } /** * Range Multiplication Query *

* Time-Complexity: O(log(n)) * * @param from from index * @param to to index * @author Diogo Peralta Cordeiro * @return multiplication */ public int rmq(int from, int to) { return rmq(1, from, to); } private int rmq(int v, int from, int to) { STNode n = heap[v]; // If you did a range update that contained this node, you can infer the Product without going down the tree if (n.pendingVal != null && contains(n.from, n.to, from, to)) { return (to - from + 1) * n.pendingVal; } if (contains(from, to, n.from, n.to)) { return heap[v].mul; } if (intersects(from, to, n.from, n.to)) { propagate(v); int leftMul = rmq(2 * v, from, to); int rightMul = rmq(2 * v + 1, from, to); return leftMul * rightMul; } return 1; // neutral element } /** * Range Min Query *

* Time-Complexity: O(log(n)) * * @param from from index * @param to to index * @return min */ public int rMinQ(int from, int to) { return rMinQ(1, from, to); } private int rMinQ(int v, int from, int to) { STNode n = heap[v]; // If you did a range update that contained this node, you can infer the Min value without going down the tree if (n.pendingVal != null && contains(n.from, n.to, from, to)) { return n.pendingVal; } if (contains(from, to, n.from, n.to)) { return heap[v].min; } if (intersects(from, to, n.from, n.to)) { propagate(v); int leftMin = rMinQ(2 * v, from, to); int rightMin = rMinQ(2 * v + 1, from, to); return Math.min(leftMin, rightMin); } return 1000000000; // 1e9 to avoid overflow } /** * Range Max Query *

* Time-Complexity: O(log(n)) * * @param from from index * @param to to index * @author Diogo Peralta Cordeiro * @return max */ public int rMaxQ(int from, int to) { return rMaxQ(1, from, to); } private int rMaxQ(int v, int from, int to) { STNode n = heap[v]; // If you did a range update that contained this node, you can infer the Max value without going down the tree if (n.pendingVal != null && contains(n.from, n.to, from, to)) return n.pendingVal; if (contains(from, to, n.from, n.to)) return heap[v].max; if (intersects(from, to, n.from, n.to)) { propagate(v); int leftMax = rMaxQ(2 * v, from, to); int rightMax = rMaxQ(2 * v + 1, from, to); return Math.max(leftMax, rightMax); } return -1000000000; // 1e9 to avoid overflow } /** * Range Update Operation. * With this operation you can update either one position or a range of positions with a given number. * The update operations will update the less it can to update the whole range (Lazy Propagation). * The values will be propagated lazily from top to bottom of the segment tree. * This behavior is really useful for updates on portions of the array *

* Time-Complexity: O(log(n)) * * @param from from index * @param to to index * @param value value */ public void update(int from, int to, int value) { update(1, from, to, value); } private void update(int v, int from, int to, int value) { // The Node of the heap tree represents a range of the array with bounds: [n.from, n.to] STNode n = heap[v]; /** * If the updating-range contains the portion of the current Node We lazily update it. * This means We do NOT update each position of the vector, but update only some temporal * values into the Node; such values into the Node will be propagated down to its children only when they need to. */ if (contains(from, to, n.from, n.to)) { change(n, value); } if (n.size() == 1) return; if (intersects(from, to, n.from, n.to)) { /** * Before keeping going down to the tree We need to propagate the * the values that have been temporally/lazily saved into this Node to its children * So that when We visit them the values are properly updated */ propagate(v); update(2 * v, from, to, value); update(2 * v + 1, from, to, value); n.sum = heap[2 * v].sum + heap[2 * v + 1].sum; n.mul = heap[2 * v].mul * heap[2 * v + 1].mul; n.min = Math.min(heap[2 * v].min, heap[2 * v + 1].min); n.max = Math.max(heap[2 * v].max, heap[2 * v + 1].max); } } // Propagate temporal values to children private void propagate(int v) { STNode n = heap[v]; if (n.pendingVal != null) { change(heap[2 * v], n.pendingVal); change(heap[2 * v + 1], n.pendingVal); n.pendingVal = null; //unset the pending propagation value } } // Save the temporal values that will be propagated lazily private void change(STNode n, int value) { n.pendingVal = value; n.sum = n.size() * value; n.mul = n.size() * value; n.min = value; n.max = value; array[n.from] = value; } // Test if the range1 contains range2 private boolean contains(int from1, int to1, int from2, int to2) { return from2 >= from1 && to2 <= to1; } // check inclusive intersection, test if range1[from1, to1] intersects range2[from2, to2] private boolean intersects(int from1, int to1, int from2, int to2) { return from1 <= from2 && to1 >= from2 // (.[..)..] or (.[...]..) || from1 >= from2 && from1 <= to2; // [.(..]..) or [..(..).. } // The Node class represents a partition range of the array. static class STNode { int sum, mul; int min, max; // Here we store the value that will be propagated lazily Integer pendingVal = null; int from; int to; int size() { return to - from + 1; } } }