#684 Editable Chart Range Sums

A revenue chart lets users edit any day's value and drag a selection to see the total of the selected days. Write a class RangeSums:

• new RangeSums(nums) starts with the daily values nums.
• update(index, value) sets day index to value.
• sumRange(left, right) returns the sum of days left to right, inclusive.

Both methods are called up to 3 * 10^4 times on up to 3 * 10^4 days, so each call should be O(log n).

Each example lists the calls in order, then each call's arguments. The first call creates the object with new RangeSums(…); the output lists what each call returns (null for the constructor and for methods that return nothing).

Input: ["RangeSums","sumRange","update","sumRange"]
[[[1,3,5]],[0,2],[1,2],[0,2]]
Output: [null,9,null,8]

Input: ["RangeSums","sumRange","sumRange","sumRange"]
[[[5,8,6,3,2,7,2,6]],[2,6],[0,7],[4,4]]
Output: [null,20,39,2]

Constraints

• 1 <= nums.length <= 3 * 10^4
• -100 <= nums[i], value <= 100
• 0 <= index < nums.length
• 0 <= left <= right < nums.length