hdu 1754 I Hate It(数据结构:线段树)

#include <cstdio>
#include <iostream>
#include <algorithm>
#define MAXN 200010
#define LL long long
using namespace std;

int sum[MAXN<<2];

void pushUp(int rt) {
sum[rt] = max(sum[rt<<1], sum[rt<<1|1]);
}

void build(int l, int r, int rt) {
if(l == r) {
scanf("%d", &sum[rt]);
return ;
}
int m = (l+r)>>1;
build(l, m, rt<<1);
build(m+1, r, rt<<1|1);
pushUp(rt);
}

void update(int p, int add, int l, int r, int rt) {
if(l == r) {
sum[rt] = add;
return ;
}
int m = (l+r)>>1;
if(p <= m)
update(p, add, l, m, rt<<1);
else update(p, add, m+1, r, rt<<1|1);
pushUp(rt);
}

int query(int L, int R, int l, int r, int rt) {
if(L<=l && r<=R) {
return sum[rt];
}
int m = (l+r)>>1;
int ret = 0;
if(L <= m)
ret = max(ret, query(L, R, l, m, rt<<1));
if(R > m) {
ret = max(ret, query(L, R, m+1, r, rt<<1|1));
}
return ret;
}

int main(void) {
int m, n, a, b;
char ch;
while(scanf("%d%d", &n, &m) != EOF) {
build(1, n, 1);
while(m--) {
scanf(" %c", &ch);
scanf("%d%d", &a, &b);
if(ch == 'Q') {
cout << query(a, b, 1, n, 1) << endl;
} else {
update(a, b, 1, n, 1);
}
}
}
return 0;
}