303 Range Sum Query - Immutable
Problem:
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:
You may assume that the array does not change.
There are many calls to sumRange function.
Solutions:
public class NumArray {
int[] sums;
int[] nums;
public NumArray(int[] nums) {
this.nums = nums;
sums = new int[nums.length];
int sum = 0;
for (int i = 0; i < nums.length; i ++) {
sum += nums[i];
sums[i] = sum;
}
}
public int sumRange(int i, int j) {
return sums[j] - sums[i] + nums[i];
}
}