Create 1394.cpp

HDOJ/1394.cpp

@@ -0,0 +1,137 @@
+/// HDU 1394
+
+/// General includes
+#include <cstdio>
+#include <cstdlib>
+#include <cstring>
+
+#include <algorithm>
+using namespace std;
+
+///求数列逆序数
+inline int GetInversionNumberOfSequence(int* seq,int len)
+{
+    int ans=0;
+    for(int i=0;i<len-1;i++)
+    {
+        for(int j=i;j<len;j++)
+        {
+            if(seq[i]>seq[j])ans++;
+        }
+    }
+    return ans;
+}
+
+
+
+/// 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);
+        tree[_internal_v].val = 0;
+        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=tree[_internal_v<<1].val+tree[_internal_v<<1|1].val;
+}
+
+void update(int Pos,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=1;
+        return;
+    }
+    /// Update Deep-Loop
+    if(Pos <= tree[_internal_v<<1].rt) update(Pos,_internal_v<<1);
+    if(Pos >= tree[_internal_v<<1|1].lt) update(Pos,_internal_v<<1|1);
+    /// SegmentTree Main Algorithm
+    tree[_internal_v].val = 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+=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
+
+const int MAXN = 5005;
+int a[MAXN];
+
+int main()
+{
+    using namespace SegmentTree;
+    int n;
+    while(scanf("%d",&n)==1)
+    {
+        build(1,n);
+        int TSum=0;
+        for(int i=0;i<n;i++)
+        {
+            scanf("%d",&a[i]);
+            //a[i]+=1; /// From 0 to 1, ... From n-1 to n (Understand)
+            ///Query ? Why ??
+            TSum+=query(a[i]+1,n);
+            update(a[i]+1);
+        }
+        int MinSum=TSum;
+        for(int i=0;i<n;i++)
+        {
+            /// 当a[i]由第一个变为最后一个时,
+            /// 要加上a[i]后面大于a[i]的数的个数,
+            /// 有n-1-a[i]个，要减去a[i]后面小于a[i]的数的个数,
+            /// 有a[i]个（注意i是从0开始的）
+            TSum=TSum+n - 2*a[i] -1;
+            MinSum=min(MinSum,TSum);
+        }
+
+        printf("%d\n",MinSum);
+    }
+    return 0;
+}