Create 1754.cpp

HDOJ/1754.cpp

@@ -0,0 +1,114 @@
+/// General includes
+#include <cstdio>
+#include <cstdlib>
+#include <cstring>
+
+#include <algorithm>
+using namespace std;
+
+/// 最基础的线段树: 单点更新,区间运算(求和)
+namespace SegmentTree
+{
+
+const int MAXN = 1000100;
+const int MAXTREENODE = MAXN<<2;
+
+struct node
+{
+    int lt,rt;
+    int val;
+};
+
+node tree[MAXTREENODE];
+
+/// _internal_v is a indexer of SegmentTree. It guides the procedure to the right node.
+
+void build(int L,int R,int _internal_v=1) /// Build a tree, _internal_v is 1 by default.
+{
+    tree[_internal_v].lt=L;
+    tree[_internal_v].rt=R;
+    if(L==R)
+    {
+        scanf("%d",&tree[_internal_v].val);
+        /// Or: tree[_internal].val = VAL_BY_DEFAULT
+        return;
+    }
+    int mid=(L+R)>>1;
+    build(L,mid,_internal_v<<1);
+    build(mid+1,R,_internal_v<<1|1);/// x<<1 == x*2; x<<1|1 == x*2+1; (faster == slower)
+    /// SegmentTree Main Algorithm
+    tree[_internal_v].val=max(tree[_internal_v<<1].val,tree[_internal_v<<1|1].val);
+}
+
+void update(int Pos,int Val,int _internal_v=1)/// Update a position, _internal_v is 1 by default.
+{
+    if(tree[_internal_v].lt==tree[_internal_v].rt)
+    {
+        tree[_internal_v].val=Val;
+        return;
+    }
+    /// Update Deep-Loop
+    if(Pos <= tree[_internal_v<<1].rt) update(Pos,Val,_internal_v<<1);
+    if(Pos >= tree[_internal_v<<1|1].lt) update(Pos,Val,_internal_v<<1|1);
+    /// SegmentTree Main Algorithm
+    tree[_internal_v].val = max(tree[_internal_v<<1].val,tree[_internal_v<<1|1].val);
+}
+
+int _internal_ans;
+inline void _internal_clear_ans()
+{
+    _internal_ans=0;
+}
+inline int _internal_get_ans()
+{
+    return _internal_ans;
+}
+void basic_query(int L,int R,int _internal_v=1)/// Query A Segment [L,R] , _internal_v is 1 by default.
+{
+    if(tree[_internal_v].lt >= L && tree[_internal_v].rt <= R)
+    {
+        _internal_ans=max(_internal_ans,tree[_internal_v].val);
+        return;
+    }
+    if(L <= tree[_internal_v<<1].rt) basic_query(L,R,_internal_v<<1);
+    if(R >= tree[_internal_v<<1|1].lt) basic_query(L,R,_internal_v<<1|1);
+}
+
+int query(int L,int R)
+{
+    _internal_clear_ans();
+    basic_query(L,R);
+    return _internal_get_ans();
+}
+
+}/// End of namespace SegmentTree
+
+char str[8];
+int main()
+{
+    using namespace SegmentTree;
+    int n,q;
+    while(scanf("%d %d",&n,&q)==2)
+    {
+        build(1,n);
+        for(int i=0; i<q; i++)
+        {
+            int a,b;
+            scanf("%s %d %d",str,&a,&b);
+            switch(str[0])
+            {
+            case 'Q':
+            {
+                int ans=query(a,b);
+                printf("%d\n",ans);
+            }
+            break;
+            case 'U':
+            {
+                update(a,b);
+            }
+            }
+        }
+    }
+    return 0;
+}