Leetcode Range Sum query-immutable

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]

Sumrange (0, 2)--1

Sumrange (2, 5)-1

Sumrange (0, 5)-3

Note:

1. Assume that the array does is not a change.
2. There is many calls to sumrange function.

Problem Solving Ideas:

The simplest dynamic programming. Complexity:numarray o (n) sumrange O (1)

To solve the boundary problem, establish ACCU = new int[nums.length+1] accu[i] to represent nums[0]+...+ Nums[i-1]

Recurrence Formula:accu[i] = Accu[i-1] + nums[i-1] Base case:accu[0]= 0

Java Code:

 Public classNumarray {Private int[] accu;  PublicNumarray (int[] nums) {Accu=New int[Nums.length+1]; accu[0] = 0;  for(inti = 1; I<= nums.length; i++) {Accu[i]= Accu[i-1] + nums[i-1]; }    }     Public intSumrange (intIintj) {returnACCU[J+1]-Accu[i]; }}//Your Numarray object would be instantiated and called as such://Numarray Numarray = new Numarray (nums);//numarray.sumrange (0, 1);//Numarray.sumrange (1, 2);

Reference:

1. Https://leetcode.com/discuss/68725/5-lines-c-4-lines-python

2. Https://leetcode.com/discuss/69081/3ms-java-solution-with-array-no-special-i-0-check

Leetcode Range Sum query-immutable