ソースコード
#include<bits/stdc++.h>
using namespace std;
const int INF = 1 << 30;
struct SegmentTree
{
vector< int > seg;
int sz;
SegmentTree(int n)
{
sz = 1;
while(sz < n) sz <<= 1;
seg.assign(2 * sz - 1, INF);
}
int rmq(int a, int b, int k, int l, int r)
{
if(a >= r || b <= l) return (INF);
if(a <= l && r <= b) return (seg[k]);
return (min(rmq(a, b, 2 * k + 1, l, (l + r) >> 1),
rmq(a, b, 2 * k + 2, (l + r) >> 1, r)));
}
int rmq(int a, int b)
{
return (rmq(a, b, 0, 0, sz));
}
void update(int k, int x)
{
k += sz - 1;
seg[k] = x;
while(k > 0) {
k = (k - 1) >> 1;
seg[k] = min(seg[2 * k + 1], seg[2 * k + 2]);
}
}
};
int N, A[3000], B[3000];
int sum[3005];
int main()
{
cin >> N;
for(int i = 0; i < N; i++) cin >> A[i];
for(int i = 0; i < N; i++) cin >> B[i];
for(int i = 0; i < N; i++) sum[i + 1] += sum[i] + A[i];
vector< SegmentTree > latte(N, SegmentTree(N)), malta(N, SegmentTree(N));
int ret = INF;
auto update = [&](int x, int y, int z)
{
if(x == 0 && y == N - 1) cout << z << endl;
if(y + 1 < N) latte[x].update(y + 1, z + B[y + 1]);
if(x - 1 >= 0) malta[y].update(x - 1, z + B[x - 1]);
};
for(int i = 0; i < N; i++) update(i, i, B[i]);
for(int i = 2; i <= N; i++) {
for(int j = 0; j <= N - i; j++) {
int k = j + i - 1;
int low = j, high = k + 1;
while(high - low > 0) {
int mid = (low + high) >> 1;
int sum1 = sum[mid] - sum[j];
int sum2 = sum[k + 1] - sum[mid + 1];
if(sum1 >= sum2) high = mid;
else low = mid + 1;
}
update(j, k, min(latte[j].rmq(low, k + 1), malta[k].rmq(j, low)));
}
}
}