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poj-2299 Ultra—QuickSort(归并排序求逆序数)
Ultra-QuickSort
Time Limit: 7000MS | Memory Limit: 65536K | |
Total Submissions: 38688 | Accepted: 13950 |
Description
In this problem, you have to analyze a particular sorting algorithm. The algorithm processes a sequence of n distinct integers by swapping two adjacent sequence elements until the sequence is sorted in ascending order. For the input sequence
9 1 0 5 4 ,
Ultra-QuickSort produces the output
0 1 4 5 9 .
Your task is to determine how many swap operations Ultra-QuickSort needs to perform in order to sort a given input sequence.
Ultra-QuickSort produces the output
Your task is to determine how many swap operations Ultra-QuickSort needs to perform in order to sort a given input sequence.
Input
The input contains several test cases. Every test case begins with a line that contains a single integer n < 500,000 -- the length of the input sequence. Each of the the following n lines contains a single integer 0 ≤ a[i] ≤ 999,999,999, the i-th input sequence element. Input is terminated by a sequence of length n = 0. This sequence must not be processed.
Output
For every input sequence, your program prints a single line containing an integer number op, the minimum number of swap operations necessary to sort the given input sequence.
Sample Input
5 9 1 0 5 4 3 1 2 3 0
Sample Output
6 0
思路:
归并排序求逆序数,用作模版
代码:
#include <stdio.h> #define lld I64d #define LL __int64 #define N 1000050 LL num[N]; LL temp[N]; // 归并排序的辅助数组 LL count = 0; void Merge(LL * array, int first, int middle, int last) { int i = first, j = middle + 1, cur = 0; while(i <= middle && j <= last){ if(array[i] < array[j]) temp[cur ++] = array[i ++]; else{ temp[cur ++] = array[j ++]; count += middle - i + 1; } } while(i <= middle) temp[cur ++] = array[i ++]; while(j <= last) temp[cur ++] = array[j ++]; for (int k = 0; k < cur; k ++) array[first ++] = temp[k]; } void MergeSort(LL *array, int first, int last) { if (first == last) return ; int middle = first + (last - first) / 2; MergeSort(array, first, middle); MergeSort(array, middle+1, last); Merge(array, first, middle, last); } int main() { int n, i; while(scanf("%d", &n), n){ count = 0; for(i = 0; i < n; i ++) scanf("%lld", &num[i]); MergeSort(num, 0, n - 1); /* for(i = 0; i < n; i ++) printf("%lld ", num[i]); printf("\n"); */ printf("%lld\n", count); } return 0; }
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