LeetCode - Range Sum Query Immutable Solution - The Coding Shala

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 In this post, we will learn how to solve LeetCode's Range Sum Query Immutable Problem and its solution in Java.

Range Sum Query Immutable Problem

Given an integer array nums, find the sum of the elements between indices i and j (i ≤ j), inclusive. Implement the NumArray class: 
NumArray(int[] nums) Initializes the object with the integer array nums. int sumRange(int i, int j) Return the sum of the elements of the nums array in the range [i, j] inclusive (i.e., sum(nums[i], nums[i + 1], ... , nums[j])).

Example 1:
Input: ["NumArray", "sumRange", "sumRange", "sumRange"]
           [[[-2, 0, 3, -5, 2, -1]], [0, 2], [2, 5], [0, 5]]
Output: [null, 1, -1, -3]

Practice this problem on LeetCode: (Click Here)

Range Sum Query - Immutable Java Solution

Approach 1:
First, make a sum array that contains sum till every index then return sum[j] - sum[i-1].

Java Program: 

class NumArray {

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

 * Your NumArray object will be instantiated and called as such:
 * NumArray obj = new NumArray(nums);
 * int param_1 = obj.sumRange(i,j);

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