题目描述
输入格式
输出格式
输入样例
4
1 3 3 5
输出样例
3
题解
#include <iostream> #include <cstdio> #define MAX_N 100000 using namespace std; int n; int a[MAX_N | 1]; long long ans; void Merge_Sort(int lt, int rt) { if(lt == rt) return; int mid = lt + rt >> 1; Merge_Sort(lt, mid); Merge_Sort(mid + 1, rt); int i = lt, j = mid + 1; int b[MAX_N | 1], cnt = 0; while(i <= mid && j <= rt) { if(a[i] >= a[j]) b[++cnt] = a[i++]; else ans += mid - i + 1, b[++cnt] = a[j++]; } while(i <= mid) b[++cnt] = a[i++]; while(j <= rt) b[++cnt] = a[j++]; for(register int i = lt; i <= rt; ++i) { a[i] = b[i - lt + 1]; } return; } int main() { scanf("%d", &n); for(register int i = 1; i <= n; ++i) { scanf("%d", &a[i]); a[i] += n - i; // 重点语句 } Merge_Sort(1, n); printf("%lld", ans % 12345); return 0; }