[LintCode] Interval Sum

kelvinlee 发布于2019-08-14 16:23 / 3193人阅读

摘要：很简单的题目，不过要达到的时间，只能用前缀和的方法来做。法前缀和法推荐

Problem

Given an integer array (index from 0 to n-1, where n is the size of this array), and an query list. Each query has two integers [start, end]. For each query, calculate the sum number between index start and end in the given array, return the result list.

Example

For array [1,2,7,8,5], and queries [(0,4),(1,2),(2,4)], return [23,9,20]

Challenge

O(logN) time for each query

Note

很简单的题目，不过要达到O(logn)的时间，只能用前缀和的方法来做。

Solution

1. muggle法

public class Solution {
    public ArrayList intervalSum(int[] A, 
                                       ArrayList queries) {
        ArrayList res = new ArrayList ();
        for (int i = 0; i < queries.size(); i++) {
            int start = queries.get(i).start;
            int end = queries.get(i).end;
            res.add(sum(A, start, end));
        }
        return res;
    }
    public long sum(int[] A, int start, int end) {
        long sum = 0;
        for (int i = start; i <= end; i++) {
            sum += A[i];
        }
        return sum;
    }
}

2. 前缀和法（推荐）

public class Solution {
    public ArrayList intervalSum(int[] A, 
                                       ArrayList queries) {
        ArrayList res = new ArrayList();
        long[] preSum = new long[A.length];
        long sum = 0;
        for (int i = 0; i < A.length; i++) {
            sum += A[i];
            preSum[i] = sum;
        }
        for (Interval i: queries) {
            if (i.start == 0) {
                res.add(preSum[i.end]);
            }
            else {
                res.add(preSum[i.end] - preSum[i.start-1]);
            }
        }
        return res;
    }
}

云服务器 GPU云服务器 Interval LintCode LintCode134_LRU sum

文章版权归作者所有，未经允许请勿转载,若此文章存在违规行为，您可以联系管理员删除。

转载请注明本文地址：https://www.ucloud.cn/yun/66196.html

[LeetCode/LintCode] Merge Intervals

摘要：方法上没太多难点，先按所有区间的起点排序，然后用和两个指针，如果有交集进行操作，否则向后移动。由于要求的，就对原数组直接进行操作了。时间复杂度是的时间。 Problem Given a collection of intervals, merge all overlapping intervals. Example Given intervals => merged intervals...

gougoujiang 2019-08-14 15:16 评论0 收藏0
[LintCode] Interval Minimum Number

摘要：这道题目是筛选出数组中的最小值，存入新数组。因此，联想到和系列的题目，对于的处理，使用线段树是非常有效的方法。之前我们创建的线段树，有和两个。参照这个参数，可以考虑在这道题增加一个的参数，代表每个结点的最小值。 Problem Given an integer array (index from 0 to n-1, where n is the size of this array),...

taowen 2019-08-14 16:23 评论0 收藏0
[LintCode/LeetCode] Meeting Rooms

Problem Given an array of meeting time intervals consisting of start and end times [[s1,e1],[s2,e2],...] (si < ei), determine if a person could attend all meetings. Example Given intervals = [[0,30],[...

Noodles 2019-08-16 12:34 评论0 收藏0
[LintCode] Segment Tree Query I & Segment Tree

摘要：题目是要查询到这个区间内某一点的。值是从最底层的子节点值里取最大值。因此，不用太复杂，递归就可以了。与所不同的是，对所给区间内的元素个数求和，而非筛选。这样就会出现的情况，视作本身处理。 Segment Tree Query Problem For an integer array (index from 0 to n-1, where n is the size of this ar...

vibiu 2019-08-14 16:22 评论0 收藏0
[LintCode] Teemo Attacking

Problem In LOL world, there is a hero called Teemo and his attacking can make his enemy Ashe be in poisoned condition. Now, given the Teemos attacking ascending time series towards Ashe and the poison...

whjin 2019-08-16 12:37 评论0 收藏0