时间限制:10000ms
单点时限:1000ms
内存限制:256MB
- 样例输入
-
3,1,2 1,2,3,4,5
- 样例输出
-
1 0
Description
Find a pair in an integer array that swapping them would maximally decrease the inversion count of the array. If such a pair exists, return the new inversion count; otherwise returns the original inversion count.
Definition of Inversion: Let (A[0], A[1] ... A[n], n <= 50) be a sequence of n numbers. If i < j and A[i] > A[j], then the pair (i, j) is called inversion of A.
Example:
Count(Inversion({3, 1, 2})) = Count({3, 1}, {3, 2}) = 2
InversionCountOfSwap({3, 1, 2})=>
{
InversionCount({1, 3, 2}) = 1 <-- swapping 1 with 3, decreases inversion count by 1
InversionCount({2, 1, 3}) = 1 <-- swapping 2 with 3, decreases inversion count by 1
InversionCount({3, 2, 1}) = 3 <-- swapping 1 with 2 , increases inversion count by 1
}
Input
Input consists of multiple cases, one case per line.Each case consists of a sequence of integers separated by comma.
Output
For each case, print exactly one line with the new inversion count or the original inversion count if it cannot be reduced.
思路,此题采用的是暴力法,不过改进的一个地方是计算InversionCount的算法,采用的是合并排序,时间复杂度是O(nlogn)
import java.util.Scanner; public class Main { static int InversionCount ; public static void main(String[] args) { int T,t; Scanner jin = new Scanner(System.in); while (jin.hasNext()) { String str = jin.next(); String[] argstr = str.split(","); int[] num = new int[argstr.length]; int[] tmp = new int[argstr.length]; for (int i = 0; i < num.length; i++) { num[i] = Integer.parseInt(argstr[i]); tmp[i] = Integer.parseInt(argstr[i]); } InversionCount = 0; MergeSort(tmp, 0, tmp.length-1); int ret = InversionCount; for (int i = 0; i < num.length; i++) tmp[i] = num[i]; for (int i = 0; i < num.length-1; i++) { for (int j = i+1; j < num.length; j++) { if (num[i] > num[j]) { int tmpnum = num[i]; num[i] = num[j]; num[j] = tmpnum; InversionCount = 0; MergeSort(num, 0, num.length-1); ret = Math.min(ret, InversionCount); for (int k = 0; k < num.length; k++) num[k] = tmp[k]; } } } System.out.println(ret); } } public static void MergeSort(int[] array, int lhs, int rhs) { if (lhs < rhs) { int mid = lhs + ((rhs - lhs)>>1); MergeSort(array, lhs, mid); MergeSort(array, mid+1, rhs); Merge(array, lhs, mid, rhs); } } public static void Merge(int[] array, int lhs, int mid, int rhs) { int[] tmp = new int[rhs-lhs+1]; int i = lhs, j = mid+1; int k = 0; while(i <= mid && j <= rhs) { if (array[i] > array[j]) { InversionCount += mid-i+1; tmp[k++] = array[j++]; } else { tmp[k++] = array[i++]; } } while(i <= mid) { tmp[k++] = array[i++]; } while(j <= rhs) { tmp[k++] = array[j++]; } for (i = 0; i < k; i++) { array[i+lhs] = tmp[i]; } tmp = null; } }
【微软2014实习生及秋令营技术类职位在线测试】题目3 : Reduce inversion count,布布扣,bubuko.com