303. Range Sum Query - Immutable

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

Dynamic Programming

public class NumArray {    int sum [];    public NumArray(int[] nums) {        sum = new int [nums.length + 1];        sum[0] = 0;        for(int i = 0; i < nums.length; i++){            sum[i + 1] = nums[i] + sum[i];        }    }    public int sumRange(int i, int j) {        return sum[j + 1] - sum[i];    }}

Example:

Given nums = [-2, 0, 3, -5, 2, -1]sumRange(0, 2) -> 1sumRange(2, 5) -> -1sumRange(0, 5) -> -3

Note:

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