1function buildPrefixSum(nums) {
2 const prefix = new Array(nums.length + 1).fill(0);
3 for (let i = 0; i < nums.length; i++)
4 prefix[i + 1] = prefix[i] + nums[i];
5 return prefix;
6}
7function rangeSum(prefix, l, r) {
8 return prefix[r + 1] - prefix[l];
9}