用线段树维护区间最大值，支持修改单点的值。
#include <cstdio>
#include <cstring>
#include <algorithm>
using namespace std;
#define LL(x) (x<<1)
#define RR(x) (x<<1|1)
const int maxn = 200005;
struct node
{
int l, r;
int Max;
}tree[maxn*4];
int num[maxn];
void build(int rt, int l, int r)
{
tree[rt].l = l;
tree[rt].r = r;
if(tree[rt].l == tree[rt].r) {
tree[rt].Max = num[l];
return ;
}
int mid = (tree[rt].l + tree[rt].r)>>1;
build(LL(rt), l, mid);
build(RR(rt), mid+1, r);
tree[rt].Max = max(tree[LL(rt)].Max, tree[RR(rt)].Max);
}
void update(int rt, int pos, int val) {
if(tree[rt].l == tree[rt].r) {
tree[rt].Max = val;
return ;
}
int mid = (tree[rt].l + tree[rt].r)>>1;
if(pos <=mid) update(LL(rt), pos, val);
else update(RR(rt), pos, val);
tree[rt].Max = max(tree[LL(rt)].Max, tree[RR(rt)].Max);
}
int query(int rt, int l, int r) {
if(l <= tree[rt].l && r >= tree[rt].r) {
return tree[rt].Max;
}
int mid = (tree[rt].l + tree[rt].r)>>1;
int ret = 0;
if(l <= mid) ret =max(ret, query(LL(rt), l, r) );
if(r > mid ) ret =max(ret, query(RR(rt), l, r) );
return ret;
}
int main()
{
int n, m, i, a, b, val;
while(scanf("%d%d",&n,&m)!=EOF)
{
for(i=1; i<=n; ++i) scanf("%d",&num[i]);
build(1,1,n);
char op[10];
while(m--)
{
scanf("%s",op);
if(op[0]==‘Q‘) {
scanf("%d%d",&a,&b);
printf("%d\n", query(1,a,b));
}
else if(op[0]==‘U‘) {
scanf("%d%d",&a,&val);
update(1,a,val);
}
}
}
return 0;
}