hdu 1754 I Hate It 【线段树】

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题目链接：http://acm.hdu.edu.cn/showproblem.php?pid=1754
题意：中文题
解析：线段树，单点修改，区间查询

#include <bits/stdc++.h>
using namespace std;
const int maxn = 200000+500;
struct node
{int l,r;int maxx;
}tree[4*maxn];
int a[maxn];
void push_up(int i)
{tree[i].maxx = max(tree[i<<1].maxx,tree[i<<1|1].maxx);
}
void build(int i,int l,int r)
{tree[i].l = l,tree[i].r = r;tree[i].maxx = 0;if(l==r){tree[i].maxx = a[r];return ;}int mid = (l+r)>>1;build(i<<1,l,mid);build(i<<1|1,mid+1,r);push_up(i);
}
void update(int i,int pos,int val)
{int l = tree[i].l;int r = tree[i].r;if(l==r && l==pos){tree[i].maxx = val;return ;}int mid = (l+r)>>1;if(mid>=pos)update(i<<1,pos,val);elseupdate(i<<1|1,pos,val);push_up(i);
}
int query(int i,int l,int r)
{int L = tree[i].l;int R = tree[i].r;if(l<=L && R<=r)return tree[i].maxx;int mid = (L+R)>>1;int ans = 0;if(mid<r)ans = query(i<<1|1,l,r);if(mid>=l)ans = max(ans,query(i<<1,l,r));return ans;
}
int main(void)
{int n,m;while(~scanf("%d %d",&n,&m)){for(int i=1;i<=n;i++)scanf("%d",&a[i]);build(1,1,n);while(m--){char op[10];int x,y;scanf("%s %d %d",op,&x,&y);if(op[0]=='U')update(1,x,y);elseprintf("%d\n",query(1,x,y));}}return 0;
}

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