Lintcode: Interval Sum II

Posted

tags:

篇首语:本文由小常识网(cha138.com)小编为大家整理,主要介绍了Lintcode: Interval Sum II相关的知识,希望对你有一定的参考价值。

Given an integer array in the construct method, implement two methods query(start, end) and modify(index, value):

For query(start, end), return the sum from index start to index end in the given array.
For modify(index, value), modify the number in the given index to value
Have you met this question in a real interview? Yes
Example
Given array A = [1,2,7,8,5].

query(0, 2), return 10.
modify(0, 4), change A[0] from 1 to 4.
query(0, 1), return 6.
modify(2, 1), change A[2] from 7 to 1.
query(2, 4), return 14.
Note
We suggest you finish problem Segment Tree Build, Segment Tree Query and Segment Tree Modify first.

Challenge
O(logN) time for query and modify.

Segment Tree:

 1 public class Solution {
 2     /* you may need to use some attributes here */
 3     class SegmentTreeNode {
 4         long sum;
 5         int start;
 6         int end;
 7         SegmentTreeNode left;
 8         SegmentTreeNode right;
 9         SegmentTreeNode(int start, int end) {
10             this.sum = 0;
11             this.start = start;
12             this.end = end;
13             this.left = null;
14             this.right = null;
15         }
16     }
17     
18     SegmentTreeNode root;
19 
20     /**
21      * @param A: An integer array
22      */
23     public Solution(int[] A) {
24         // write your code here
25         if (A == null || A.length==0) return;
26         root = build(A, 0, A.length-1);
27         
28     }
29     
30     public SegmentTreeNode build(int[] A, int start, int end) {
31         SegmentTreeNode cur = new SegmentTreeNode(start, end);
32         if (start == end) cur.sum = A[start];
33         else {
34             int mid = (start + end)/2;
35             cur.left = build(A, start, mid);
36             cur.right = build(A, mid+1, end);
37             cur.sum = cur.left.sum + cur.right.sum;
38         }
39         return cur;
40     }
41     
42     /**
43      * @param start, end: Indices
44      * @return: The sum from start to end
45      */
46     public long query(int start, int end) {
47         // write your code here
48         return queryTree(root, start, end);
49     }
50     
51     public long queryTree(SegmentTreeNode cur, int start, int end) {
52         if (cur.start==start && cur.end==end) return cur.sum;
53         int mid = (cur.start + cur.end)/2;
54         if (end <= mid) return queryTree(cur.left, start, end);
55         else if (start > mid) return queryTree(cur.right, start, end);
56         else return queryTree(cur.left, start, mid) + queryTree(cur.right, mid+1, end);
57     }
58     
59     /**
60      * @param index, value: modify A[index] to value.
61      */
62     public void modify(int index, int value) {
63         // write your code here
64         modifyTree(root, index, value);
65     }
66     
67     public void modifyTree(SegmentTreeNode cur, int index, int val) {
68         if (cur.start == cur.end) {
69             cur.sum = val;
70             return;
71         }
72         int mid = (cur.start + cur.end)/2;
73         if (index <= mid) modifyTree(cur.left, index, val);
74         else modifyTree(cur.right, index, val);
75         cur.sum = cur.left.sum + cur.right.sum;
76     }
77 }

 

以上是关于Lintcode: Interval Sum II的主要内容,如果未能解决你的问题,请参考以下文章

Lintcode: Interval Sum

Lintcode206 Interval Sum solution 题解

Lintcode206 Interval Sum solution 题解

lintcode-medium-Combination Sum II

[LintCode] Subarray Sum II

Lintcode153.Combination Sum II