题意:求逆序对
解题思路:1)树状数组 + 离散化
解题代码:
1 // File Name: a.cpp 2 // Author: darkdream 3 // Created Time: 2014年08月05日 星期二 12时05分09秒 4 5 #include<vector> 6 #include<list> 7 #include<map> 8 #include<set> 9 #include<deque> 10 #include<stack> 11 #include<bitset> 12 #include<algorithm> 13 #include<functional> 14 #include<numeric> 15 #include<utility> 16 #include<sstream> 17 #include<iostream> 18 #include<iomanip> 19 #include<cstdio> 20 #include<cmath> 21 #include<cstdlib> 22 #include<cstring> 23 #include<ctime> 24 #define LL long long 25 26 using namespace std; 27 int n , k ; 28 LL sum = 0 ; 29 int lowbit(int x) 30 { 31 return x&(-x); 32 } 33 struct node{ 34 int num, s,rs ; 35 }a[100005]; 36 int num[100005]; 37 int getsum(int x){ 38 int sum = 0 ; 39 while(x >= 1) 40 { 41 sum += num[x]; 42 x -= lowbit(x); 43 } 44 return sum ; 45 } 46 void update(int x) 47 { 48 while(x <= n ) 49 { 50 num[x] ++ ; 51 x += lowbit(x); 52 } 53 return; 54 } 55 int cmp(node x ,node y ) 56 { 57 return x.num < y.num; 58 } 59 int cmp1(node x, node y) 60 { 61 return x.s < y.s; 62 } 63 int main(){ 64 while(scanf("%d %d",&n,&k)!= EOF) 65 { 66 memset(num,0,sizeof(num)); 67 for(int i =1;i <= n;i ++) 68 { 69 scanf("%d",&a[i].num); 70 a[i].s = i ; 71 } 72 sort(a+1,a+1+n,cmp); 73 int t = 1; 74 a[1].rs = 1; 75 for(int i = 2;i <= n;i ++) 76 { 77 if(a[i].num == a[i-1].num) 78 a[i].rs = t ; 79 else { 80 t++; 81 a[i].rs = t; 82 } 83 } 84 sort(a+1,a+1+n,cmp1); 85 sum = 0 ; 86 for(int i = 1;i <= n;i ++) 87 { 88 sum += (getsum(n)- getsum(a[i].rs)); 89 update(a[i].rs); 90 } 91 if(sum > k) 92 cout << sum-k << endl; 93 else printf("0\n"); 94 } 95 return 0; 96 }
2)归并排序
HDU4911 Inversion 解题报告
时间: 2024-10-15 11:38:18