Title Description
Two numbers in the array, if a number is greater than the front behind the figures, the two numbers form a reverse pair. Enter an array, this array P. finds the total number of reverse pair P and outputs the result modulo 1000000007. I.e., the output P% 1000000007
Enter a description:
Title ensure the same number of the input array is not
data range:
50% of the data, size <= 10 ^ 4
75% of the data, size <= 10 ^ 5
100% of the data, size <= 2 * 10 ^ 5
Example 1
Entry
1,2,3,4,5,6,7,0
Export
7
Solution:
such as:
(A) the length of the array 4 into two sub-arrays of length 2;
(B) the length of the array 2 is decomposed into two sub-arrays of Chengdu 1;
(c) the length of the sub-array 1 is
combined sorting and counting reverse order
;
(D) the length of the subarray 2 merge, sorting, and counting on the reverse;
import java.util.Arrays; public class Solution { public static int InversePairs(int [] array) { if(array==null||array.length==0) { return 0; } // int[] copy = new int[array.length]; // for(int i=0;i<array.length;i++) // { // copy[i] = array[i]; // } int[] copy = Arrays.copyOf(array, array.length); int count = InversePairsCore(array,copy,0,array.length-1);//数值过大求余 return count; } private static int InversePairsCore(int[] array, int[] copy, int l, int r) { if(l==r){ return 0; } int mid = l + ((r-l)>>1); int lCount = InversePairsCore(array,copy, l, mid)%1000000007; int rCount = InversePairsCore(array,copy, mid+1, r)%1000000007; int count = 0; int i=mid; int j=r; int locCopy = r; while(i>=l && j>mid){ if(array[i]>array[j]){ count += j-mid; //此注意边界 copy[locCopy--] = array[i--]; if(count>=1000000007)//数值过大求余 { count%=1000000007; } }else{ copy[locCopy--] = array[j--]; } } while(i>=l){ copy[locCopy--] = array[i--]; } while(j>mid){ copy[locCopy] = array[j--]; } for(int s=l; s<=r; s++){ array[s] = copy[s]; } return (lCount+rCount+count)%1000000007; } public static void main(String[] args) { int[] arr = {1,5,0,3,2}; int res = InversePairs(arr); System.out.println(res); } }