Range Sum Query - Immutable

LeetCode: https://leetcode.com/problems/range-sum-query-immutable/

Given an integer array nums, handle multiple queries of the form sumRange(left, right) returning the sum of elements between left and right inclusive.

1class NumArray:
2    def __init__(self, nums: List[int]):
3        self.pref = [0]
4        for x in nums:
5            self.pref.append(self.pref[-1] + x)
6            
7    def sumRange(self, left: int, right: int) -> int:
8        return self.pref[right + 1] - self.pref[left]

Subarray Sum Equals K

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

Step 1 / 6

Step 1:

Build pref where pref[i] = sum of nums[0..i-1]. Start with pref[0]=0.

Pointers: i=0

Focus: select @ [0]