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复习:线段树功能很强大,但是敲起来不如树状数组简洁(但是但是线段树仍然赛高(`・ω・´))。所以这次复习下树状数组的区间最值写法。原理类似区间求和,单点修改。
有一个博主写的博客不错,之前也是学习的他的。安利下,自己就不写教程了,这里练下手,复习下~
AC代码:
#include<bits/stdc++.h>
#define IO ios_base::sync_with_stdio(0),cin.tie(0),cout.tie(0)
#define pb(x) push_back(x)
#define all(x) x.begin(),x.end()
#define sz(x) (int)(x).size()
#define sc(x) scanf("%d",&x)
#define pr(x) printf("%d\n",x);
using namespace std;
typedef long long ll;
const int mod = 1e9+7;
const double PI = 4*atan(1.0);
const int maxm = 1e8+5;
const int maxn = 2e5+5;
const int INF = 0x3f3f3f3f;
int c[maxn];
int a[maxn];
int lowbit(int x) {return x&(-x);}
void update(int x,int n)
{
for(int i=x;i<=n;i+=lowbit(i))
{
c[i] = a[i];
for(int j=1;j<lowbit(i);j<<=1)
c[i] = max(c[i],c[i-j]);
}
}
int query(int l,int r)
{
int ans = -1;
while(r>=l)
{
ans = max(ans,a[r]);
r--;
for(;r-lowbit(r)>=l;r-=lowbit(r))
ans = max(ans,c[r]);
}
return ans;
}
int main()
{
#ifdef LOCAL_FILE
freopen("in.txt","r",stdin);
#endif // LOCAL_FILE
int n,m;
while(~scanf("%d %d",&n,&m))
{
for(int i=1;i<=n;i++)
{
sc(a[i]);
update(i,n);
}
while(m--)
{
char ch[2];
scanf("%s",ch);
if(ch[0] == 'Q')
{
int l,r;
sc(l);sc(r);
pr(query(l,r));
}
else if(ch[0] == 'U')
{
int pos,val;
sc(pos);sc(val);
a[pos] = val;
update(pos,n);
}
}
}
return 0;
}