Range Sum Query - Immutable

描述

Given an integer array nums, find the sum of the elements between indices i and j (i ≤ j), inclusive.

Example:

Given nums = [-2, 0, 3, -5, 2, -1]

  1. sumRange(0, 2) -> 1
  2. sumRange(2, 5) -> -1
  3. sumRange(0, 5) -> -3

Note:

  • You may assume that the array does not change.
  • There are many calls to sumRange function.

    分析

令状态f[i]为0到i元素之间的和，则状态转移方程为 f[i] = f[i-1] + nums[i]。f[i]本质上是累加和，有了f[i]，则范围[i,j]之间的和等于f[j] - f[i-1]。

代码

相关题目

原文: https://soulmachine.gitbooks.io/algorithm-essentials/content/cpp/dp/range-sum-query-immutable.html