дерево сумм снизу

#include <bits/stdc++.h>
using namespace std;
int n, a[100500], inf = -1000000000, t[500500];
int main(){
	freopen("C.in", "r", stdin);
	freopen("C.out", "w", stdout);
	cin >> n;
	for(int i = 1; i <= n; u++){
		cin >> a[i];
	}
	sz = 1;
	while(sz < n){
		sz *= 2;
	}
	for(int i = sz; i <= n + sz - 1; i++){
		t[i] = a[i - sz + 1];
	}
	for(int i = sz + n; i <= sz + sz - 1; i++){
		t[i] = -inf;
	}
	for(int i = sz - 1; i >= 1; i--){
		t[i] = t[i * 2] + t[i * 2 + 1];
	}
}