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
Constraints:
You may assume that the array does not change. There are many calls to sumRange function. 0 <= nums.length <= 10^4 -10^5 <= nums[i] <= 10^5 0 <= i <= j < nums.length
public class NumArray {
int[] sumArr;
public NumArray(int[] nums) {
if(nums.Length==0){
return;
}
sumArr = new int[nums.Length];
sumArr[0]=nums[0];
for(int i=1;i<nums.Length;i++){
sumArr[i]=sumArr[i-1]+nums[i];
}
}
public int SumRange(int i, int j) {
if(sumArr==null){
return 0;
}
if(i==0){
return sumArr[j];
}
return sumArr[j]-sumArr[i-1];
}
}
/**
* Your NumArray object will be instantiated and called as such:
* NumArray obj = new NumArray(nums);
* int param_1 = obj.SumRange(i,j);
*/Time Complexity: O(n)
Space Complexity: O(n)
