HDU 1754
线段树入门题,找下手感
#include <cstdio>
#include <iostream>
#include <algorithm>
#include <cstring>
#include <queue>
using namespace std;
const int maxn= 2e5+5;
const int maxm= 5e3+5;
const int maxl= maxn<<2;
int tree[maxl], ar[maxn];
int a, b;
inline LChild(int x)
{
return x<<1;
}
inline RChild(int x)
{
return x<<1|1;
}
void Build(int rt, int l, int r)
{
if (l== r){
tree[rt]= ar[l];
return;
}
int lc= LChild(rt), rc= RChild(rt);
int mid= (l+r)>>1;
Build(lc, l, mid);
Build(rc, mid+1, r);
tree[rt]= tree[lc] > tree[rc] ? tree[lc] : tree[rc];
}
void Update(int rt, int l, int r)
{
if (l== r){
tree[rt]= ar[l];
return;
}
int lc= LChild(rt), rc= RChild(rt);
int md= (l+r)>>1;
if (l<= a && a<= md){
Update(lc, l, md);
}
if (md+1<= a && a<= r){
Update(rc, md+1, r);
}
tree[rt]= tree[lc] > tree[rc] ? tree[lc] : tree[rc];
}
int Query(int rt, int l, int r)
{
if (a<= l && r<= b){
return tree[rt];
}
int md= (l+r)>>1, ans= -1, t= -1;
if (a<= md){
t= Query(LChild(rt), l, md);
if (t> ans){
ans= t;
}
}
if (md+1<= b){
t= Query(RChild(rt), md+1, r);
if (t> ans){
ans= t;
}
}
return ans;
}
int main(int argc, char const *argv[])
{
int n, m;
char op;
while (EOF!= scanf("%d %d", &n, &m)){
for(int i= 1; i<= n; ++i){
scanf("%d", ar+i);
}
memset(tree, -1, sizeof(tree));
Build(1, 1, n);
while (m--){
scanf(" %c", &op);
if ('U'== op){
scanf("%d %d", &a, &b);
ar[a]= b;
Update(1, 1, n);
}
else{
scanf("%d %d", &a, &b);
cout<<Query(1, 1, n)<<endl;
}
}
}
return 0;
}