Java Program for Range sum queries without updates
Given an array arr of integers of size n. We need to compute sum of elements from index i to index j. The queries consisting of i and j index values will be executed multiple times.
Examples:
Input : arr[] = {1, 2, 3, 4, 5}
i = 1, j = 3
i = 2, j = 4
Output : 9
12
Input : arr[] = {1, 2, 3, 4, 5}
i = 0, j = 4
i = 1, j = 2
Output : 15
5
// Java program to find sum between two indexes // when there is no update. import java.util.*; import java.lang.*; class GFG { public static void preCompute(int arr[], int n, int pre[]) { pre[0] = arr[0]; for (int i = 1; i < n; i++) pre[i] = arr[i] + pre[i - 1]; } // Returns sum of elements in arr[i..j] // It is assumed that i <= j public static int rangeSum(int i, int j, int pre[]) { if (i == 0) return pre[j]; return pre[j] - pre[i - 1]; } public static void main(String[] args) { int arr[] = { 1, 2, 3, 4, 5 }; int n = arr.length; int pre[] = new int[n]; preCompute(arr, n, pre); System.out.println(rangeSum(1, 3, pre)); System.out.println(rangeSum(2, 4, pre)); } } // Code Contributed by Mohit Gupta_OMG <(0_o)> |
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Output:
9 12
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