HDU 1754 I Hate It

线段树Push_Up入门，注意一下递归的条件不然就会像我一样WA4发。
（PS：这道题目卡cin）

#include
#include
#include
#include
#define LL long long
#define uLL unsigned long long 
#define fio ios::sync_with_stdio(false);cin.tie(0);cout.tie(0);
#define fix fixed << setprecision(2)
int max(int x, int y) {if(x > y) return x; return y;}
int min(int x, int y) {if(x > y) return y; return x;}
using namespace std;
int mod = 1e9 + 7;
const int INF = 1e9 + 7;
const double PI = 3.1415927;
struct node {
  int l, r;
  int sum;
};
node tr[500005 * 4];
int n, m;
int cnt;
int a[500005];
void Push_Up(int i) {
  tr[i].sum = max(tr[i * 2].sum, tr[i * 2 + 1].sum);
}
inline void Build(int i, int l, int r) {
  tr[i].l = l, tr[i].r = r;
  if(l == r) {
    tr[i].sum = a[l];
    return ;
  }
  int mid = (l + r) >> 1;
  Build(i * 2, l, mid);
  Build(i * 2 + 1, mid + 1, r);
  Push_Up(i);
}
inline int Search(int i, int l, int r) {
  if(tr[i].l == l && tr[i].r == r) {
    return tr[i].sum;
  }
  int ans = 0, mid = (tr[i].l + tr[i].r) >> 1;;
  if(mid >= r) {
    return Search(i * 2, l, r);
  } else if(l > mid) {
    return Search(i * 2 + 1, l, r);
  } else {
    return max(Search(i * 2, l, mid), Search(i * 2 + 1, mid + 1, r));
  }
}
inline void Add(int i, int dis, int k) {
  if(tr[i].l == tr[i].r) {
    tr[i].sum = k;
    return ;
  }
  if(dis <= tr[i * 2].r) Add(i * 2, dis, k);
  else Add(i * 2 + 1, dis, k);
  Push_Up(i);
  return ;
}
int main() {
  while(~scanf("%d %d", &n, &m)) {
    for(int i = 1; i <= n; ++i) {
      scanf("%d", &a[i]);
    }
    Build(1, 1, n);
    while(m--) {
      char op;
      int x, y;
      scanf(" %c %d %d", &op, &x, &y);
      if(op == 'Q') {
        printf("%d\n", Search(1, x, y));
      } else {
        Add(1, x, y);
      }
    }
  }
  return 0;
}

纪念一下刚学线段树的题目^ v ^.
还有入门题luogu的树状数组模板1and2，可以去尝试尝试。