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- #include <iostream>
- #include <vector>
- #include <algorithm>
- #include <set>
- #include <cmath>
- #include <map>
- #include <cstring>
- using namespace std;
- const int maxn = 2e5 + 10;
- int arr[maxn];
- long long segment_tree[3 * maxn];
- void build_tree(int L, int R, int position) {
- if(L == R) {
- segment_tree[position] = arr[L];
- }
- else {
- int middle = (L + R) / 2;
- build_tree(L, middle
- , 2 * position);
- build_tree(middle + 1, R, 2 * position + 1);
- segment_tree[position] = segment_tree[2 * position] + segment_tree[2 * position + 1];
- }
- }
- long long query(int L, int R, int position, int i, int j) {
- if(i <= L and R <= j) {
- return segment_tree[position];
- }
- if(R < i or j < L) {
- return 0;
- }
- int middle = (L + R) / 2;
- return query(L, middle, 2 * position, i, j) + query(middle + 1, R, 2 * position + 1, i, j);
- }
- int main() {
- int n, q;
- cin >> n >> q;
- for(int i = 0; i < n; i++) {
- cin >> arr[i];
- }
- build_tree(0, n - 1, 1); // building the tree O(N log(N))
- for(int i = 0; i < q; i++) {
- int a, b;
- cin >> a >> b;
- a--; b--;
- cout << query(0, n - 1, 1, a, b) << endl;
- }
- return 0;
- }
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