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.
public class NumArray {
int sum[] = null;
public NumArray(int[] nums) {
if(nums.length == 0){
return;
}
sum = new int[nums.length];
sum[0] = nums[0];
for(int i = 1; i<nums.length; i++){
sum[i] = sum[i-1] + nums[i];
}
}
public int sumRange(int i, int j) {
if(sum == null){
return 0;
}
return sum[j] - (i==0?0:sum[i-1]);
}
}
