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segment tree for query sum.cpp
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segment tree for query sum.cpp
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#include <iostream>
using namespace std;
int sum[20];
int num[] = {0, 1, 2, 3, 4, 5, 6, 7, 8};
void build (int at, int L, int R) {
if (L == R) {
sum[at] = num[L];
return;
}
int mid = (L+R) /2;
build (2*at, L, mid);
build (2*at+1, mid+1, R);
sum[at] = sum[2*at] + sum[2*at+1];
}
void update (int at, int L, int R, int pos, int value) {
if (at == pos) {
sum[at] += value;
return;
}
int mid = (L+R) /2;
if (pos <= at) update (2*at, L, mid, pos, value);
else update (2*at+1, mid+1, R, pos, value);
sum[at] = sum[2*at] + sum[2*at+1];
}
int query (int at, int L, int R, int l, int r) {
if (L > r || R < l) return 0;
if (L >= l && R <= r) return sum[at];
int mid = (L+R) /2;
int x = query (2*at, L, mid, l, r);
int y = query (2*at+1, mid+1, R, l, r);
return x+y;
}
int main ()
{
build (1, 1, 8);
for (int i = 0; i < 20; i++) cout << sum[i] << " ";
cout << endl;
update (1, 1, 8, 3, 4);
for (int i = 0; i < 25; i++) cout << sum[i] << " ";
cout << endl;
cout << query (1, 1, 8, 2, 6) << endl;
return 0;
}