HDU 1754 I Hate It 基础线段树

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用区间值m表示这段区间的最大值，一直更新这个区间的最大值，很基础的线段树

#include<iostream>#include<stdio.h>using namespace std;#define N 200005struct node{    int l,r,m;}tree[N*4];int a[N];void build(int left,int right,int i){    tree[i].l=left;    tree[i].r=right;    if(tree[i].l==tree[i].r){        tree[i].m=a[tree[i].l];        return ;    }    int mid=(tree[i].l+tree[i].r)>>1;    build(left,mid,i*2);    build(mid+1,right,i*2+1);    tree[i].m=max(tree[i*2].m,tree[i*2+1].m);}void updata(int left,int right,int i,int val){ //   cout<<tree[i].l<<" "<<tree[i].r<<endl;    if(left==tree[i].l&&right==tree[i].r){        tree[i].m=val;        return ;    }     if(tree[i].l>left || tree[i].r<left) return ;    int mid=(tree[i].r+tree[i].l)>>1;    updata(left,right,i*2,val);    updata(left,right,i*2+1,val);    tree[i].m=max(tree[i*2].m,tree[i*2+1].m);}int ans=0;void query(int left,int right,int i){ //   cout<<"Q 4 5 "<<left<<" "<<right<<" "<<tree[3].m<<endl;    if(tree[i].l==left&&tree[i].r==right){        if(tree[i].m>ans)            ans=tree[i].m;        return ;    }    int mid=(tree[i].l+tree[i].r)>>1;    if(mid>=right)        query(left,right,i*2);    else if(mid<left)        query(left,right,i*2+1);    else{        query(left,mid,i*2);        query(mid+1,right,i*2+1);    }}int main(){//    freopen("in.txt","r",stdin);    int m,n,x,y;    char t[5];    while(~scanf("%d%d",&n,&m)){        for(int i=1;i<=n;i++)            scanf("%d",&a[i]);        build(1,n,1);        while(m--){            scanf("%s %d%d",t,&x,&y);//            cout<<t<<" "<<x<<" "<<y<<endl;            if(t[0]=='Q'){                ans=0;                query(x,y,1);                printf("%d\n",ans);            }            else{                updata(x,x,1,y);            }        }    }}

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