题目描述
提供一下线段树的做法
样例
#include <iostream>
using namespace std;
const int N = 200010, M = 18;
int n, m;
int w[N];
struct Node{
int l, r;
int v;
}tr[N * 4];
void pushup(Node &root, Node &l, Node &r)
{
root.v = max(l.v, r.v);
}
void pushup(int u)
{
tr[u].v = max(tr[u << 1].v, tr[u << 1 | 1].v);
}
void build(int u, int l, int r)
{
if(l == r) tr[u] = {l, r, w[l]};
else{
tr[u] = {l ,r, 0};
int mid = l + r >> 1;
build(u << 1, l , mid), build(u << 1 | 1, mid + 1, r);
pushup(u);
}
}
Node query(int u, int l, int r)
{
if(tr[u].l >= l && tr[u].r <= r) return tr[u];
else{
int mid = tr[u].l + tr[u].r >> 1;
if(r <= mid) return query(u << 1, l , r);
if(l > mid) return query(u << 1 | 1, l ,r);
else{
Node res;
auto left = query(u << 1, l , r);
auto right = query(u << 1 | 1, l, r);
pushup(res, left, right);
return res;
}
}
}
int main()
{
scanf("%d", &n);
for (int i = 1; i <= n; i ++ ) scanf("%d", &w[i]);
build(1,1, 200010);
scanf("%d", &m);
while (m -- )
{
int l, r;
scanf("%d%d", &l, &r);
printf("%d\n", query(1,l, r).v);
}
return 0;
}