HDU I Hate It

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 題目意思很簡單，很裸的線段樹。

有是一道單點更新問題，是單點更新+區間最大值。

#include <iostream>#include <algorithm>#include <cstdio>#include <cstring>using namespace std;#define L(x) (x<<1)#define R(x) (x<<1|1)#define lson lft,mid,rt << 1#define rson mid+1,rht,rt << 1 | 1#define MID(a,b) (a+((b-a)>>1))#define INF 1<<30const int MAXN = 200005;struct Node{   int lft,rht,mx;   int mid(){return MID(lft,rht);}};Node tree[4*MAXN];int y[MAXN],n,m;class Segtree{public:    void Build(int lft,int rht,int rt){        tree[rt].lft = lft; tree[rt].rht = rht;        tree[rt].mx = -INF;        if(lft == rht)           tree[rt].mx = y[lft];        else{            int mid = tree[rt].mid();            Build(lson);            Build(rson);            tree[rt].mx = max(tree[L(rt)].mx,tree[R(rt)].mx);        }    }    void Update(int pos,int rt,int val){        int lft = tree[rt].lft,rht = tree[rt].rht;        if(lft == rht){            tree[rt].mx = val;        }        else{            int mid = tree[rt].mid();            if(pos <= mid) Update(pos,L(rt),val);            else Update(pos,R(rt),val);            tree[rt].mx = max(tree[L(rt)].mx,tree[R(rt)].mx);        }   }   int Query(int st,int ed,int rt){       int lft = tree[rt].lft,rht = tree[rt].rht;       if(st <= lft&&rht <= ed) return tree[rt].mx;       else{            int mid = tree[rt].mid();            int mx1 = -INF,mx2 = -INF;            if(st <= mid) mx1 = Query(st,ed,L(rt));            if(ed > mid) mx2 = Query(st,ed,R(rt));            return max(mx1,mx2);       }   }};int main(){    while(~scanf("%d%d",&n,&m))    {        Segtree seg;        char op[5];        int a,b;        for(int i = 1;i <= n;++i)            scanf("%d",&y[i]);        seg.Build(1,n,1);        while(m--){            scanf("%s%d%d",op,&a,&b);            if(op[0] == 'Q')               printf("%d\n",seg.Query(a,b,1));            else               seg.Update(a,1,b);        }    }    return 0;}