POJ - 2299 - Ultra-QuickSort(线段树求逆序数+离散化)

题目链接：https://vjudge.net/contest/358908#problem/H

题目大意：给你一个序列，问你这个序列经过冒泡排序形成的非递减序列所需要的次数

　　很经典的线段树求逆序数的题，对于序列中的一个数字来说，把他移动到在非递减序列中的位置的交换次数就是他前面比他大的数字的数目，至于每次交换的后续性这是不用考虑的，因为这里只是说相对位置

#include<set>
#include<map>
#include<stack>
#include<queue>
#include<cmath>
#include<cstdio>
#include<cctype>
#include<string>
#include<vector>
#include<climits>
#include<cstring>
#include<cstdlib>
#include<iostream>
#include<algorithm>
#define endl '\n'
#define rtl rt<<1
#define rtr rt<<1|1
#define lson rt<<1, l, mid
#define rson rt<<1|1, mid+1, r
#define maxx(a, b) (a > b ? a : b)
#define minn(a, b) (a < b ? a : b)
#define zero(a) memset(a, 0, sizeof(a))
#define INF(a) memset(a, 0x3f, sizeof(a))
#define IOS ios::sync_with_stdio(false)
#define _test printf("~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~\n")
using namespace std;
typedef long long ll;
typedef pair<int, int> P;
typedef pair<ll, ll> P2;
const double pi = acos(-1.0);
const double eps = 1e-7;
const ll MOD =  1000000007LL;
const int INF = 0x3f3f3f3f;
const int _NAN = -0x3f3f3f3f;
const double EULC = 0.5772156649015328;
const int NIL = -1;
template<typename T> void read(T &x){
    x = 0;char ch = getchar();ll f = 1;
    while(!isdigit(ch)){if(ch == '-')f*=-1;ch=getchar();}
    while(isdigit(ch)){x = x*10+ch-48;ch=getchar();}x*=f;
}
const int maxn = 1e6+10;
int arr[maxn], t[maxn], tree[maxn<<2];
void build(int rt, int l, int r) {
    tree[rt] = 0;
    if (l==r) return;
    int mid = (l+r)>>1;
    build(lson);
    build(rson);
}
void change(int pos, int rt, int l, int r) {
    if (l==r) {
        tree[rt] |= 1;
        return;
    }
    int mid = (l+r)>>1;
    pos <= mid ? change(pos, lson) : change(pos, rson);
    tree[rt] = tree[rtl] + tree[rtr];
}
ll find(int st, int ed, int rt, int l, int r) {
    if (st<=l && ed>=r) 
        return  tree[rt];
    int mid = (l+r)>>1; ll ans = 0;
    if (st<=mid)
        ans += find(st, ed, lson);
    if (ed>mid)
        ans += find(st, ed, rson);
    return ans;
}
int main(void) {
    int n;
    while(~scanf("%d", &n) && n) {
        for (int i = 1; i<=n; ++i) {
            scanf("%d", &arr[i]);
            t[i] = arr[i];
        }
        sort(t+1, t+n+1);
        int last = unique(t+1, t+n+1)-t;
        for (int i = 1; i<=n; ++i)
            arr[i] = lower_bound(t+1, t+last, arr[i])-t;
        ll sum = 0;
        for (int i = 1; i<=n; ++i) {
            sum += find(arr[i], last, 1, 1, last);
            change(arr[i], 1, 1, last);
        }
        printf("%lld\n", sum);
        build(1, 1, last);
    }
    return 0;
}