hdu-1754 I Hate It---线段树模板题

题目链接：

http://acm.hdu.edu.cn/showproblem.php?pid=1754

题目大意：

求区间最大值+单点修改

解题思路：

直接套用模板即可

 #include<bits/stdc++.h>
 #define MID(l, r) (l + (r - l) / 2)
 #define lson(o) (o * 2)
 #define rson(o) (o * 2 + 1)
 using namespace std;
 typedef long long ll;
 const int INF = 1e9 +;
 const int maxn = 1e6 + ;
 int a[maxn];
 struct node
 {
     int l, r, mmax, mmin, sum;
 }tree[maxn];
 void build(int o, int l, int r)
 {
     tree[o].l = l, tree[o].r = r;
     if(l == r)
     {
         tree[o].mmax = tree[o].mmin = tree[o].sum = a[l];
         return;
     }
     int m = MID(l, r);
     int lc = lson(o), rc = rson(o);
     build(lc, l, m);
     build(rc, m + , r);
     tree[o].mmax = max(tree[lc].mmax, tree[rc].mmax);
     tree[o].mmin = min(tree[lc].mmin, tree[rc].mmin);
     tree[o].sum = tree[lc].sum + tree[rc].sum;
 }
 int ql, qr;//查询区间[ql, qr]中的max,min,sum
 int ans_max, ans_min, ans_sum;
 void query_init()//查询前，将全局变量初始化
 {
     ans_max = -INF;
     ans_min = INF;
     ans_sum = ;
 }
 void query(int o)
 {
     if(ql <= tree[o].l && qr >= tree[o].r)//[L, R]包含在[ql, qr]区间内，直接用该节点的信息，达到线段树查询快的操作
     {
         ans_max = max(ans_max, tree[o].mmax);
         ans_min = min(ans_min, tree[o].mmin);
         ans_sum += tree[o].sum;
         return;
     }
     int m = MID(tree[o].l, tree[o].r);
     if(ql <= m)query(lson(o));
     if(qr > m)query(rson(o));
 }
 //单点更新，a[p] = v;
 int p, v;
 void update(int o)
 {
     if(tree[o].l == tree[o].r)
     {
         tree[o].mmax = v;
         tree[o].mmin = v;
         tree[o].sum = v;
         return;
     }
     int m = MID(tree[o].l, tree[o].r);
     int lc = lson(o), rc = rson(o);
     if(p <= m)update(lc);
     else update(rc);
     tree[o].mmax = max(tree[lc].mmax, tree[rc].mmax);
     tree[o].mmin = min(tree[lc].mmin, tree[rc].mmin);
     tree[o].sum = tree[lc].sum + tree[rc].sum;
 }
 int main()
 {
     int n, m;
     while(scanf("%d%d", &n, &m) != EOF)
     {
         for(int i = ; i <= n; i++)scanf("%d", &a[i]);
         build(, , n);
         char s[];
         int x, y;
         while(m--)
         {
             scanf("%s%d%d", s, &x, &y);
             if(s[] == 'Q')
             {
                 ql = x, qr = y;
                 query_init();
                 query();
                 printf("%d\n", ans_max);
             }
             else if(s[] == 'U')
             {
                 p = x, v = y;
                 update();
             }
         }
     }
     return ;
 }