This page explains Java solution to problem Range Sum Query - Immutable
using Prefix array
.
Given an integer array nums, find the sum of the elements between indices i
and j
(i ≤ j)
, inclusive.
Input: nums = [-2, 0, 3, -5, 2, -1]
Output:
sumRange(0, 2) -> 1
sumRange(2, 5) -> -1
sumRange(0, 5) -> -3
package com.vc.easy;
class RangeSumQueryImmutable {
int[] prefixArr;
public RangeSumQueryImmutable(int[] nums) {
prefixArr = new int[nums.length + 1];
for(int i = 0; i < nums.length; i++) {
prefixArr[i + 1] = prefixArr[i] + nums[i];
}
}
public int sumRange(int i, int j) {
return prefixArr[j + 1] - prefixArr[i];
}
}
/**
* Your NumArray object will be instantiated and called as such:
* NumArray obj = new NumArray(nums);
* int param_1 = obj.sumRange(i,j);
*/
O(N) to generate prefix sum array Where
N is total number of elements in an input array
O(1) to get range sum
O(N) Where
N is total number of elements in an input array