From c5c309b935e33ecdfecffec50a93b72b0cbcd6e5 Mon Sep 17 00:00:00 2001
From: Zengtudor <Zengtudor@outlook.com>
Date: Sun, 31 Aug 2025 16:17:34 +0800
Subject: [PATCH] =?UTF-8?q?feat:=20=E6=B7=BB=E5=8A=A0P5200=E9=A2=98?=
 =?UTF-8?q?=E8=A7=A3=E5=AE=9E=E7=8E=B0=EF=BC=8C=E4=BD=BF=E7=94=A8=E6=A0=91?=
 =?UTF-8?q?=E7=8A=B6=E6=95=B0=E7=BB=84=E8=AE=A1=E7=AE=97=E9=80=86=E5=BA=8F?=
 =?UTF-8?q?=E5=AF=B9?=
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

实现了一个使用树状数组计算逆序对数量的算法，用于解决P5200题目。通过维护树状数组来高效计算区间和，从而确定每个元素的逆序对数量。
---
 src/8/31/P5200.cpp | 65 ++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 65 insertions(+)
 create mode 100644 src/8/31/P5200.cpp

diff --git a/src/8/31/P5200.cpp b/src/8/31/P5200.cpp
new file mode 100644
index 0000000..e0c9b13
--- /dev/null
+++ b/src/8/31/P5200.cpp
@@ -0,0 +1,65 @@
+#include <cstdint>
+#include <iostream>
+#include <istream>
+#include <vector>
+using ll = int64_t;
+
+ll n;
+std::vector<ll> v,t,ans;
+
+#define pv(v)do{std::cout<<#v<<" :"<<(v)<<"\n";}while(0)
+
+static inline constexpr ll lowbit(ll n){
+    return n&(-n);
+}
+
+static inline void set(ll idx,ll addval){
+    while(idx<=n){
+        t[idx]+=addval;
+        idx+=lowbit(idx);
+    }
+}
+
+static inline ll getsfx(ll idx){
+    ll res=0;
+    while(idx){
+        res+=t[idx];
+        idx-=lowbit(idx);
+    }
+    return res;
+}
+
+static inline ll getrange(ll l,ll r){
+    return getsfx(r)-getsfx(l-1);
+}
+
+int main(){
+    std::iostream::sync_with_stdio(false);
+    std::cin.tie(nullptr);
+
+    std::cin>>n;
+    v.resize(n+1);
+    t.resize(n+1);
+    ans.reserve(n+1);
+    for(ll i=1;i<=n;++i){
+        std::cin>>v[i];
+    }
+    ll idx=n;
+    for(;idx>=2 && v[idx-1]<=v[idx];--idx);
+    // pv(idx);
+    for(ll i=idx;i<=n;i++){
+        set(v[i], 1);
+    }
+    ll sum=0;
+    for(ll i=1;i<idx;i++){
+        ll add = idx-i-1 + getrange(1, v[i]);
+        sum+=add;
+        ans.push_back(add);
+        set(v[i], 1);
+    }
+    std::cout<<idx-1<<"\n";
+    for(ll i:ans){
+        std::cout<<i<<" ";
+    }
+    std::cout<<"\n";
+}
\ No newline at end of file