From 4ae88a860b69c30dc5d9cc2893e05c29e89cf713 Mon Sep 17 00:00:00 2001
From: Kirito <1362050620@qq.com>
Date: Sat, 7 May 2016 19:40:20 +0800
Subject: [PATCH] Create 2492_cnblogs.cpp

From http://www.cnblogs.com/qiufeihai/archive/2012/03/12/2391988.html
---
 HDOJ/2492_cnblogs.cpp | 117 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 117 insertions(+)
 create mode 100644 HDOJ/2492_cnblogs.cpp

diff --git a/HDOJ/2492_cnblogs.cpp b/HDOJ/2492_cnblogs.cpp
new file mode 100644
index 0000000..8cac02e
--- /dev/null
+++ b/HDOJ/2492_cnblogs.cpp
@@ -0,0 +1,117 @@
+#include <set>
+#include <map>
+#include <list>
+#include <cmath>
+#include <ctime>
+#include <deque>
+#include <queue>
+#include <stack>
+#include <cstdio>
+#include <string>
+#include <vector>
+#include <cctype>
+#include <cstring>
+#include <sstream>
+#include <fstream>
+#include <cstdlib>
+#include <cassert>
+#include <iostream>
+#include <algorithm>
+ 
+using namespace std;
+//Constant Declaration
+/*--------------------------*/
+//#define LL long long 
+#define LL __int64
+const int M=100001;
+const int INF=1<<30;
+const double EPS = 1e-11;
+const double PI = acos(-1.0);
+/*--------------------------*/
+// some essential funtion
+/*----------------------------------*/
+void Swap(int &a,int &b){   int t=a;a=b;b=t; }
+int Max(int a,int b){   return a>b?a:b;  }
+int Min(int a,int b){   return a<b?a:b;  }
+int Gcd(int a,int b){   while(b){b ^= a ^=b ^= a %= b;}  return a; }
+/*----------------------------------*/
+//for (i = 0; i < n; i++)
+/*----------------------------------*/
+
+LL c[M];
+int a[M];
+int left_lower[M], right_lower[M];//分别是，在第i个数左右边，比第i个数小的个数
+int n = 100000;
+
+
+int LowBit(int x)
+{
+    return x&(-x);
+}
+
+int Sum(int k)
+{
+    int sum = 0;
+    while (k > 0)
+    {
+        sum += c[k];
+        k -= LowBit(k);
+    }
+    return sum;
+}
+
+void Update(int k, int sc)
+{
+    while (k <= 100000)
+    {
+        c[k] += sc;
+        k += LowBit(k);
+    }
+}
+
+
+ 
+int main()
+{
+ //freopen("in.txt","r",stdin);
+ //freopen("out.txt","w",stdout);
+ int t, case1 = 0;
+ scanf("%d", &t);
+ int m;
+ int i, j;
+ int num;
+ //scanf("%d%d", &n, &m);
+ while (t--)
+ {
+    scanf("%d", &num);
+    memset(c, 0, sizeof(c));
+    memset(left_lower, 0, sizeof(left_lower));
+    memset(right_lower, 0, sizeof(right_lower));
+    for (i = 1; i <= num; i++)
+    {
+        scanf("%d", &a[i]);
+        left_lower[i] += Sum(a[i] - 1);///Sum(a[i] - 1)：插入该数前，区间1到a[i]-1的总个数
+        Update(a[i], 1);
+    }
+    
+    memset(c, 0, sizeof(c));
+    for (i = num; i > 0; i--)//顺序插入
+    {
+        right_lower[i] += Sum(a[i] - 1);
+        Update(a[i], 1);
+    }
+
+    LL ans = 0;
+    
+    for (i = 1; i <= num; i++)//逆序插入
+    {
+        ans += left_lower[i]*(num - i - right_lower[i]);//由于只能求比其小的个数，可以用i右边的总个数见减比他小的来求比他大的个数。
+        ans += (i - 1 - left_lower[i])*right_lower[i];//
+    }
+
+    printf("%I64d\n", ans);
+ }
+ 
+
+ return 0;
+}