hdu 1754 I Hate It（最简单的线段树）

#include<iostream>
#include<cstring>
#include<cmath>
#include<cstdio>
#include<algorithm>
#include <queue>
using namespace std;

const int maxn = 200005;
const int oo = 0xfffffff;

#define L_CHILD rt<<1, begin, mid
#define R_CHILD rt<<1|1, mid + 1, end

int segTree[maxn*4];

void pushUp(int rt)
{
segTree[rt] = max(segTree[2*rt], segTree[2*rt+1]);
}
void build(int rt, int begin, int end)
{
if(begin == end) {
scanf("%d", segTree + rt);
return ;
}
int mid = begin + end >> 1;
build(L_CHILD);
build(R_CHILD);
pushUp(rt);
}

int query(int rt, int begin, int end, int left, int right)
{
if(left > end || right < begin) {
return -oo;
}
if(left <= begin && end <= right) {
return segTree[rt];
}
int mid = begin + end >> 1;
int p1 = query(L_CHILD, left, right);
int p2 = query(R_CHILD, left, right);
return max(p1, p2);
}
void update(int rt, int begin, int end, int idx, int val)
{
if(begin == end) {
segTree[rt] = val;
return ;
}
int mid = begin + end >> 1;
if(idx <= mid) {
update(L_CHILD, idx, val);
}
else {
update(R_CHILD, idx, val);
}
pushUp(rt);
}
int main()
{
int n, m, x, y;
char ch;
while (scanf("%d%d", &n, &m) != EOF) {
build(1, 1, n);
while (m --) {
scanf(" %c%d%d", &ch, &x, &y);
if(ch == 'Q') {
printf("%d\n", query(1,1,n,x,y));
}
else {
update(1, 1, n, x, y);
}
}
}
return 0;
}