hdu1754线段树维护区间最大值

#include <iostream>#include <cstdio>using namespace std;#define MAXN 200005int N,M;int grade[MAXN];struct node{    int left;    int right;    int max;}Tree[MAXN*20];int Build(int start,int end,int root){    Tree[root].left = start;    Tree[root].right = end;    if(start == end)    {        Tree[root].max = grade[start];        return Tree[root].max;    }    int mid = (start + end)/2;    int a = Build(start,mid,root*2);    int b = Build(mid+1,end,(root*2)+1);    return Tree[root].max = max(a,b);}int find(int start,int end,int root){    if(start > Tree[root].right || end < Tree[root].left)        return 0;    if(start <= Tree[root].left && Tree[root].right <= end)        return Tree[root].max;    int a = find(start,end,root*2);    int b = find(start,end,(root*2)+1);    return max(a,b);}int update(int root,int pos,int value){    if(pos < Tree[root].left || pos > Tree[root].right)        return Tree[root].max;        if(Tree[root].left == pos && Tree[root].right == pos)        return Tree[root].max = value;    int a = update(root*2,pos,value);    int b = update((root*2)+1,pos,value);    Tree[root].max = max(a,b);    return Tree[root].max;}int main(){    while(scanf("%d%d",&N,&M)!=EOF)    {        for(int i = 1; i <= N; i++)        {            scanf("%d",&grade[i]);        }        Build(1,N,1);        char ch;        int A,B;        while(M--)        {            getchar();            scanf("%c%d%d",&ch,&A,&B);            if(ch == 'Q')                cout<<find(A,B,1)<<endl;            else if(ch == 'U')            {                grade[A] = B;                update(1,A,B);            }                    }    }    return 0;}