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| 1 | +package Java; |
| 2 | + |
| 3 | +import java.util.Scanner; |
| 4 | + |
| 5 | +public class SegmentTree { |
| 6 | + private final int MAX= 1000*1000; |
| 7 | + |
| 8 | + private final int [] originalValues = new int[MAX]; |
| 9 | + private final int [] segmentSum = new int[MAX * 4]; |
| 10 | + |
| 11 | + //Get sum of range [x,y] over segment [left, right] with segId |
| 12 | + int getSum(int segId, int left, int right, int x, int y){ |
| 13 | + if ((y < left) || (right < x)) { |
| 14 | + //no intersection |
| 15 | + return 0; |
| 16 | + } else { |
| 17 | + //Two ranges somehow intersects. |
| 18 | + if ((x <= left) && (right <= y)) { |
| 19 | + //we need all values of [left, right] |
| 20 | + return segmentSum[segId]; |
| 21 | + } else { |
| 22 | + //Partly intersects |
| 23 | + final int mid = (left+right)/2; |
| 24 | + //Get sum of range [x,y] over first half of segment: [left, mid] |
| 25 | + final int sumLeft = getSum(segId*2, left, mid, x, y); |
| 26 | + //Get sum of range [x,y] over second half of segment: [mid+1, right] |
| 27 | + final int sumRight = getSum(segId*2+1, mid+1, right, x, y); |
| 28 | + |
| 29 | + return sumLeft + sumRight; |
| 30 | + } |
| 31 | + } |
| 32 | + } |
| 33 | + |
| 34 | + //Update the value of p-th element, for range [left,right] with segId |
| 35 | + void update(int segId, int left, int right, int p, int value) { |
| 36 | + if (left == right) { |
| 37 | + //it's a node, so sum is equal to the value |
| 38 | + segmentSum[segId] = value; |
| 39 | + } else { |
| 40 | + final int mid = (left+right)/2; |
| 41 | + if(p <= mid) { |
| 42 | + //continue updating for only the first half of segment [left, mid] |
| 43 | + update(segId*2, left, mid, p, value); |
| 44 | + } |
| 45 | + else { |
| 46 | + //continue updating for only the second half of segment [mid+1, right] |
| 47 | + update(segId*2+1, mid+1, right, p, value); |
| 48 | + } |
| 49 | + //Since either half is updated, we also keep the segment updated |
| 50 | + segmentSum[segId] = segmentSum[segId*2] + segmentSum[segId*2+1]; |
| 51 | + } |
| 52 | + } |
| 53 | + |
| 54 | + //Build for range [left,right] |
| 55 | + void build(int id, int left, int right){ |
| 56 | + if(left == right) { |
| 57 | + //it's a node, so sum is equal to the element |
| 58 | + segmentSum[id] = originalValues[left]; |
| 59 | + } else { |
| 60 | + final int mid = (left+right)/2; |
| 61 | + //build for range [left, mid] |
| 62 | + build(id*2, left, mid); |
| 63 | + //build for range [mid+1, right] |
| 64 | + build(id*2+1, mid+1, right); |
| 65 | + |
| 66 | + //total sum of segment id is calculated from it's two children |
| 67 | + segmentSum[id] = segmentSum[id*2] + segmentSum[id*2 + 1]; |
| 68 | + } |
| 69 | + } |
| 70 | + |
| 71 | + private void run() { |
| 72 | + final Scanner scan = new Scanner(System.in); |
| 73 | + System.out.println("Please enter the number of elements and number of queries:"); |
| 74 | + final int n = scan.nextInt(); |
| 75 | + final int queryNum = scan.nextInt(); |
| 76 | + |
| 77 | + System.out.println(String.format("Please enter the %d elements.",n)); |
| 78 | + for(int i=1; i<=n; i++) { |
| 79 | + originalValues[i] = scan.nextInt(); |
| 80 | + } |
| 81 | + |
| 82 | + //Build the tree and calculate the sums. |
| 83 | + build(1, 1, n); |
| 84 | + |
| 85 | + System.out.println(String.format("Please enter the %d queries. Op x y.",queryNum)); |
| 86 | + System.out.println("Op=1 to get sum of interval [x,y]."); |
| 87 | + System.out.println("Op=2 to get update value of x-th element to y."); |
| 88 | + for (int query=0; query < queryNum ; query+=1) { |
| 89 | + final int operation = scan.nextInt(); |
| 90 | + final int x = scan.nextInt(); |
| 91 | + final int y = scan.nextInt(); |
| 92 | + if (operation == 1) { |
| 93 | + //Print the sum of segment [x,y]. We start from segment [1,n] with id=1 |
| 94 | + System.out.println(getSum(1, 1, n, x, y)); |
| 95 | + } else { |
| 96 | + //Update the value of x-th element to y. |
| 97 | + //We recursively update the sum starting from segment [1,n] with id=1 |
| 98 | + update(1, 1, n, x, y); |
| 99 | + } |
| 100 | + } |
| 101 | + } |
| 102 | + /* |
| 103 | + Sample input: |
| 104 | + 6 6 |
| 105 | + 3 4 1 6 3 3 |
| 106 | + 1 1 4 |
| 107 | + 1 2 5 |
| 108 | + 2 4 2 |
| 109 | + 1 4 6 |
| 110 | + 2 1 13 |
| 111 | + 1 1 6 |
| 112 | +
|
| 113 | + Sample output: |
| 114 | + 14 |
| 115 | + 14 |
| 116 | + 8 |
| 117 | + 26 |
| 118 | + */ |
| 119 | + |
| 120 | + public static void main(String[] args) { |
| 121 | + new SegmentTree().run(); |
| 122 | + } |
| 123 | + |
| 124 | +} |
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