LeetCode Range Sum Query - Immutable

 1 public class NumArray {
 2     private int [] dp;
 3     public NumArray(int[] nums) {
 4         dp = new int[nums.length+1]; //dp[i]表示从nums[0]到nums[i-1]的和
 5         for(int i = 1; i<=nums.length; i++){
 6             dp[i] = dp[i-1] + nums[i-1];
 7         }
 8     }
 9 
10     public int sumRange(int i, int j) {
11         return dp[j+1] - dp[i];
12     }
13 }
14 
15 // Your NumArray object will be instantiated and called as such:
16 // NumArray numArray = new NumArray(nums);
17 // numArray.sumRange(0, 1);
18 // numArray.sumRange(1, 2);