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algo_class_count_inversions.cpp
112 lines (99 loc) · 2.29 KB
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algo_class_count_inversions.cpp
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#include<stdio.h>
#include<math.h>
#include<iostream>
#include<sstream>
#include<algorithm>
#include<functional>
#include<vector>
#include<bitset>
#include<set>
#include<map>
#include <string.h>
#include <iomanip>
#define forl(i,init, max) for(int i = init; i < max; i++)
#define vi std::vector<int>
#define mtsi std::multiset<int, std::greater<int> >
#define si std::set<int>
#define ss std::set<std::string>
#define mi std::map<int, int>
#define mci std::map<char, int>
#define mic std::map<int, char>
#define mmi std::multimap<int, int>
#define msi std::map<std::string, int>
#define INF 1<<30;
//#define DEBUG true
#ifdef DEBUG
#define out printf
#else
#define out
#endif
//returns true if a is smaller than b
int count_inversions(std::vector<int> &v)
{
int count = 0;
for(int i = 0; i < v.size() - 1; i++)
for(int j = i+1; j < v.size(); j++)
if(v[i] > v[j])
count++;
return count;
}
long long int merge_and_count(std::vector<int> &v, int s, int mid, int e, std::vector<int> &c)
{
int k = s;
int i = s;
int j = mid;
long long int count = 0;
while(k < e && i < mid && j < e) {
if(v[i] <= v[j]) {
c[k] = v[i];
i++;
}
else {
c[k] = v[j];
count += (mid-i);
j++;
}
k++;
}
while(i < mid) {
c[k] = v[i];
i++;
k++;
}
while(j < e) {
c[k] = v[j];
j++;
k++;
}
for(int i = s; i < e; i++) {
v[i] = c[i];
}
return count;
}
long long int sort_and_count(std::vector<int> &v, int s, int e, std::vector<int> &c)
{
if (s >= e - 1) { //if only one element
return 0;
}
int mid = (s + e) / 2;
long long int x = sort_and_count(v, s, mid, c);
long long int y = sort_and_count(v, mid, e, c);
long long int z = merge_and_count(v, s, mid, e, c);
return x + y + z;
}
int main(int argc, char **argv)
{
out("Starting...\n");
int m;
std::vector<int> v;
while(scanf("%d", &m) != EOF)
{
v.push_back(m);
}
printf("size=%d\n", v.size());
std::vector<int> c;
c.resize(v.size());
//printf("inversions=%d\n", count_inversions(v));
printf("inversions2=%lld\n", sort_and_count(v, 0, v.size(), c));
return 0;
}