学步园

简单线段树

#include<stdio.h>
#define N 200002
int start,end,a[N];
struct tree
{
    int left,right,maxnum;
}p[N*3];
int max(int a,int b)
{
    if(a>b)return a;
    return b;
}
void insert(int l,int r,int i)
{
    p[i].left=l;p[i].right=r;
    if(l==r)
    {
        p[i].maxnum=a[l];return ;
    }
    int mind=(l+r)/2;
    insert(l,mind,i*2);
    insert(mind+1,r,i*2+1);
    p[i].maxnum=max(p[i*2].maxnum,p[i*2+1].maxnum);
}
int find(int l,int r,int i)
{
    if(p[i].left==l&&p[i].right==r)return p[i].maxnum;
    int mind=(p[i].left+p[i].right)/2;
    if(l>mind)
       return     find(l,r,i*2+1);
    else if(r<=mind)
        return find(l,r,i*2);
    else
    {
        int x,y;
        x=find(l,mind,i*2);
        y=find(mind+1,r,i*2+1);
        return max(x,y);
    }
}
void xiugai(int l,int r,int i)
{
    if(l==r)
    {
        p[i].maxnum=end;return;
    }
    int mind=(l+r)/2;
    if(start<=mind)
        xiugai(l,mind,i*2);
    else xiugai(mind+1,r,i*2+1);
        p[i].maxnum=max(p[i*2].maxnum,p[i*2+1].maxnum);
}
    
int main()
{
    int i,n,m;
    char ch;
    while(scanf("%d%d",&n,&m)!=EOF)
    {
        for(i=1;i<=n;i++)
            scanf("%d",&a[i]);
        insert(1,n,1);
        getchar();
        for(i=0;i<m;i++)
        {
            scanf("%c%d%d",&ch,&start,&end);
            getchar();
            if(ch=='Q')
                printf("%d\n",find(start,end,1));
            else
                xiugai(1,n,1);
        }
    }
    return 0;
}