hdu 1754 线段树 单点更新 水

题意：求一段区间内的最大值，和对原来的数组进行改变

做法：入门级的线段树...

#include <iostream>#include <cstdio>#include <cstring>#define LMT 200002#define left l,m,x<<1#define right m+1,r,x<<1|1using namespace std;int smax[LMT<<2];int max(int a,int b){    return a>b?a:b;}void build(int l,int r,int x){    if(l==r)    {        scanf("%d",&smax[x]);        return;    }    int m=(l+r)>>1;    build(left);    build(right);    smax[x]=max(smax[x<<1],smax[x<<1|1]);}void update(int pos,int key,int l,int r,int x){    if(l==r)    {        smax[x]=key;        return;    }    int m=(l+r)>>1;    if(pos<=m)update(pos,key,left);    if(pos>m)update(pos,key,right);    smax[x]=max(smax[x<<1],smax[x<<1|1]);}int equery(int L,int R,int l,int r,int x){    if(L<=l&&r<=R)return smax[x];    int a=-1,b=-1,m=(l+r)>>1;    if(L<=m)a=equery(L,R,left);    if(R>m)b=equery(L,R,right);    return max(a,b);}int main(){    char ord[3];    int n,q;    while(~scanf("%d%d",&n,&q))    {        build(1,n,1);        while(q--)        {            int a,b;            scanf("%s",ord);            if(strcmp(ord,"Q")==0)            {                scanf("%d%d",&a,&b);                printf("%d\n",equery(a,b,1,n,1));            }            else            {                scanf("%d%d",&a,&b);                update(a,b,1,n,1);            }        }    }    return 0;}