[Leetcode] Range Sum Query — Immutable
Published in
1 min readJul 8, 2022
Basic example implementation of dynamic programming.
Description
Given an integer array nums
, handle multiple queries of the following type:
- Calculate the sum of the elements of
nums
between indicesleft
andright
inclusive whereleft <= right
.
Implement the NumArray
class:
NumArray(int[] nums)
Initializes the object with the integer arraynums
.int sumRange(int left, int right)
Returns the sum of the elements ofnums
between indicesleft
andright
inclusive (i.e.nums[left] + nums[left + 1] + ... + nums[right]
).
Examples
Example 1:
Input
["NumArray", "sumRange", "sumRange", "sumRange"]
[[[-2, 0, 3, -5, 2, -1]], [0, 2], [2, 5], [0, 5]]
Output
[null, 1, -1, -3]Explanation
NumArray numArray = new NumArray([-2, 0, 3, -5, 2, -1]);
numArray.sumRange(0, 2); // return (-2) + 0 + 3 = 1
numArray.sumRange(2, 5); // return 3 + (-5) + 2 + (-1) = -1
numArray.sumRange(0, 5); // return (-2) + 0 + 3 + (-5) + 2 + (-1) = -3
Solution
A trivial but useful technique. dp[i] represents sum from 0 to i. Set base at top, traverse nums to find val on new index, and add up former sum to get new.
- code
ref: https://maxming0.github.io/2021/06/16/Range-Sum-Query-Immutable/