[Hihocoder] binary and merge sort in reverse order

Time limit:10000msSingle Point time limit:1000msMemory Limit:256MB

description

We knew Nettle was playing "Battleship これ" on the previous, last, and upper back. After a bitter struggle, nettle again got a lot of boats.
This day nettle is checking its fleet list:

As we can see, the ship's default sort is the rank parameter. But in fact a ship's fire value and the level of the relationship is not big, so there will be a ship than B ship grade, but a ship fire is lower than the case of B ship. For example, the 77-stage dragon to two firepower is less than the 55-level of the XI-Li two.
Now that the nettle will give all the ship's firepower in order of rank, please calculate how many pairs of ships meet the above mentioned situation.

Tip: High firepower is fierce!

Input

Line 1th: an integer n. N indicates the number of ships, 1≤n≤100,000
Line 2nd: n integers, the number of I indicates the fire value of the ship with low rank a[i],1≤a[i]≤2^31-1.

Output

Line 1th: An integer that indicates how many pairs of ships meet "a ship is higher than B ship, but a ship's firepower is lower than ship B."

Sample input

101559614248 709366232 500801802 128741032 1669935692 1993231896 369000208 381379206 962247088 237855491

Sample output

27

Import Java.util.arrays;import Java.util.scanner;public class Main {long res = 0;private void sort (int start,int end,int[] ARR) {if (start>=end) return;int mid = (start+end)/2;sort (Start,mid,arr); sort (mid+1,end,arr); merge (Start,end,arr) ;} private void merge (int start,int end,int[]arr) {int mid = (start+end)/2;int insert[] = new Int[mid-start+1];insert = Arrays . Copyofrange (arr, start, mid+1); int idx = Start;int left = 0;int right = Mid+1;while (Left<=insert.length-1&&ri Ght<=end) {if (Arr[right]<insert[left]) {arr[idx++] = arr[right++];} Else{res + = right-(mid+1); arr[idx++]=insert[left++];}} while (left<=insert.length-1) {arr[idx++] = insert[left++];res+= right-(mid+1);}} public static void Main (String args[]) {/*scanner sc = null;try {sc = new Scanner (New FileInputStream ("D://desktop//test.tx T "));} catch (FileNotFoundException e) {//TODO auto-generated catch Blocke.printstacktrace ();} */scanner sc = new Scanner (system.in); int num = Sc.nextint (); int []arr = new Int[num];for (int i=0;i<num;i++) {Arr[i] = Sc.nextint ();} Main main = new main (); main.res = 0;main.sort (0,arr.length-1,arr); System.out.println (Main.res);}}

[Hihocoder] binary and merge sort in reverse order