线段树-入门

Java代码

3. /**
4. * 线段树入门
5. * 问题：已知线段[2,5] [4,6] [0,7]；求点2,4,7分别出现了多少次
6. * 以下代码建立的线段树用链表来保存，且树的叶子结点类似[i,i]
7. *
8. * 参考链接：http://hi.baidu.com/semluhiigubbqvq/item/be736a33a8864789f4e4ad18
9. * @author lijinnan
10. */
11. public class SegmentTreeLearn {
13. public static void main(String[] args) {
14. SegmentTree tree = new SegmentTree(0,7);
15. int[][] segments = {
16. {2, 5},
17. {4, 6},
18. {0, 7}
19. };
20. int[] targets = {2, 4, 7};
21. for (int i = 0, len = segments.length; i < len; i++) {
22. int[] segment = segments[i];
23. tree.insert(segment[0], segment[1]);
24. }
25. for(int target : targets) {
26. System.out.println(target + ":" + tree.caculateExistingTimes(target));
27. }
28. }
32. }
34. class SegmentTree {
36. //递归定义的，因此很多操作都是递归实现
37. private class Segment {
38. int left;
39. int right;
40. int count;
41. Segment leftChild;
42. Segment rightChild;
43. }
45. private Segment root;
47. public SegmentTree (int left,int right) {
48. root = new Segment();
49. build(root, left, right);
50. }
52. public void insert(int left,int right) {
53. insert(root, left, right);
54. }
56. public int caculateExistingTimes(int target) {
57. return caculateExistingTimes(root, target);
58. }
60. //从根节点开始查找叶子结点[target, target]，对经过的节点的count求和
61. private int caculateExistingTimes(Segment root,int target) {
62. int result = 0;
63. while( root.left != root.right) {
64. int rootMid = root.left + (root.right - root.left) /2;
65. result += root.count;
66. if (target <= rootMid) {
67. root = root.leftChild;
68. } else if (target > rootMid) {
69. root = root.rightChild;
70. }
71. }
72. return result;
73. }