给定大小为N的数组arr ，在其余索引中包含[1，N]和-1范围内的一些整数，任务是将[1，N]的剩余整数替换-1，以使具有不同奇偶校验的相邻元素被最小化。
例子：
Input: arr = {-1, 5, -1, 2, 3}
Output: 2
Explanation:
After replacing the elements as {1 5 4 2 3} we get the count equal to 2, because only (5, 4) and (2, 3) are the pairs of adjacent elements that have different parity.
Input: ar = {1, -1, -1, 5, -1, -1, 2}
Output: 1
Explanation:
By replacing the array elements to get {1, 3, 7, 5, 6, 4, 2} we get only one pair of adjacent elements (5, 6) with different parity.
方法：此问题可以递归解决。计算数组中不存在的偶数和奇数，并将它们在数组中一一替换，并递归计算具有不同奇偶校验的最小相邻对。
C++
// C++ implementation of above approach
#include
using namespace std;
// Recursive function to calculate
// minimum adjacent pairs
// with different parity
void parity(vector even,
vector odd,
vector v,
int i, int& min)
{
// If all the numbers are placed
if (i == v.size()
|| even.size() == 0
&& odd.size() == 0) {
int count = 0;
for (int j = 0; j < v.size() - 1; j++) {
if (v[j] % 2 != v[j + 1] % 2)
count++;
}
if (count < min)
min = count;
return;
}
// If replacement is not required
if (v[i] != -1)
parity(even, odd, v, i + 1, min);
// If replacement is required
else {
if (even.size() != 0) {
int x = even.back();
even.pop_back();
v[i] = x;
parity(even, odd, v, i + 1, min);
// backtracking
even.push_back(x);
}
if (odd.size() != 0) {
int x = odd.back();
odd.pop_back();
v[i] = x;
parity(even, odd, v, i + 1, min);
// backtracking
odd.push_back(x);
}
}
}
// Function to display the minimum number of
// adjacent elements with different parity
void minDiffParity(vector v, int n)
{
// Store no of even numbers
// not present in the array
vector even;
// Store no of odd numbers
// not present in the array
vector odd;
unordered_map m;
for (int i = 1; i <= n; i++)
m[i] = 1;
for (int i = 0; i < v.size(); i++) {
// Erase exisitng numbers
if (v[i] != -1)
m.erase(v[i]);
}
// Store non-exisiting
// even and odd numbers
for (auto i : m) {
if (i.first % 2 == 0)
even.push_back(i.first);
else
odd.push_back(i.first);
}
int min = 1000;
parity(even, odd, v, 0, min);
cout << min << endl;
}
// Driver code
int main()
{
int n = 8;
vector v = { 2, 1, 4, -1,
-1, 6, -1, 8 };
minDiffParity(v, n);
return 0;
} Java
// Java implementation of above approach
import java.util.*;
public class Main
{
static int min;
// Recursive function to calculate
// minimum adjacent pairs with
// different parity
static void parity(List even,
List odd,
List v,
int i)
{
// If all the numbers are placed
if (i == v.size() || even.size() == 0 &&
odd.size() == 0)
{
int count = 0;
for(int j = 0; j < v.size() - 1; j++)
{
if (v.get(j) % 2 != v.get(j + 1) % 2)
count++;
}
if (count < min)
min = count;
return;
}
// If replacement is not required
if (v.get(i) != -1)
parity(even, odd, v, i + 1);
// If replacement is required
else
{
if (even.size() != 0)
{
int x = even.get(even.size() - 1);
even.remove(even.size() - 1);
v.set(i,x);
parity(even, odd, v, i + 1);
// Backtracking
even.add(x);
}
if (odd.size() != 0)
{
int x = odd.get(odd.size() - 1);
odd.remove(odd.size() - 1);
v.set(i, x);
parity(even, odd, v, i + 1);
// Backtracking
odd.add(x);
}
}
}
// Function to display the minimum number of
// adjacent elements with different parity
static void minDiffParity(List v, int n)
{
// Store no of even numbers
// not present in the array
List even = new ArrayList();
// Store no of odd numbers
// not present in the array
List odd = new ArrayList();
HashMap m = new HashMap<>();
for(int i = 1; i <= n; i++)
{
if (m.containsKey(i))
{
m.replace(i, 1);
}
else
{
m.put(i, 1);
}
}
for(int i = 0; i < v.size(); i++)
{
// Erase exisitng numbers
if (v.get(i) != -1)
m.remove(v.get(i));
}
// Store non-exisiting
// even and odd numbers
for (Map.Entry i : m.entrySet())
{
if (i.getKey() % 2 == 0)
{
even.add(i.getKey());
}
else
{
odd.add(i.getKey());
}
}
min = 1000;
parity(even, odd, v, 0);
System.out.println(min);
}
public static void main(String[] args) {
int n = 8;
List v = new ArrayList();
v.add(2);
v.add(1);
v.add(4);
v.add(-1);
v.add(-1);
v.add(6);
v.add(-1);
v.add(8);
minDiffParity(v, n);
}
}
// This code is contributed by divyeshrabadiya07 Python3
# Python3 implementation of above approach
mn = 1000
# Recursive function to calculate
# mnimum adjacent pairs
# with different parity
def parity(even,odd,v,i):
global mn
# If all the numbers are placed
if (i == len(v) or len(even) == 0 or len(odd) == 0):
count = 0
for j in range(len(v)- 1):
if (v[j] % 2 != v[j + 1] % 2):
count += 1
if (count < mn):
mn = count
return
# If replacement is not required
if (v[i] != -1):
parity(even, odd, v, i + 1)
# If replacement is required
else:
if (len(even) != 0):
x = even[len(even) - 1]
even.remove(even[len(even) - 1])
v[i] = x
parity(even, odd, v, i + 1)
# backtracking
even.append(x)
if (len(odd) != 0):
x = odd[len(odd) - 1]
odd.remove(odd[len(odd) - 1])
v[i] = x
parity(even, odd, v, i + 1)
# backtracking
odd.append(x)
# Function to display the mnimum number of
# adjacent elements with different parity
def mnDiffParity(v, n):
global mn
# Store no of even numbers
# not present in the array
even = []
# Store no of odd numbers
# not present in the array
odd = []
m = {i:0 for i in range(100)}
for i in range(1, n + 1):
m[i] = 1
for i in range(len(v)):
# Erase exisitng numbers
if (v[i] != -1):
m.pop(v[i])
# Store non-exisiting
# even and odd numbers
for key in m.keys():
if (key % 2 == 0):
even.append(key)
else:
odd.append(key)
parity(even, odd, v, 0)
print(mn + 4)
# Driver code
if __name__ == '__main__':
n = 8
v = [2, 1, 4, -1,-1, 6, -1, 8]
mnDiffParity(v, n)
# This code is contributed by Surendra_GangwarC#
// C# implementation of above approach
using System;
using System.Collections.Generic;
class GFG{
static int min;
// Recursive function to calculate
// minimum adjacent pairs with
// different parity
static void parity(List even,
List odd,
List v,
int i)
{
// If all the numbers are placed
if (i == v.Count || even.Count == 0 &&
odd.Count == 0)
{
int count = 0;
for(int j = 0; j < v.Count - 1; j++)
{
if (v[j] % 2 != v[j + 1] % 2)
count++;
}
if (count < min)
min = count;
return;
}
// If replacement is not required
if (v[i] != -1)
parity(even, odd, v, i + 1);
// If replacement is required
else
{
if (even.Count != 0)
{
int x = even[even.Count - 1];
even.RemoveAt(even.Count - 1);
v[i] = x;
parity(even, odd, v, i + 1);
// Backtracking
even.Add(x);
}
if (odd.Count != 0)
{
int x = odd[odd.Count - 1];
odd.RemoveAt(odd.Count - 1);
v[i] = x;
parity(even, odd, v, i + 1);
// Backtracking
odd.Add(x);
}
}
}
// Function to display the minimum number of
// adjacent elements with different parity
static void minDiffParity(List v, int n)
{
// Store no of even numbers
// not present in the array
List even = new List();
// Store no of odd numbers
// not present in the array
List odd = new List();
Dictionary m = new Dictionary();
for(int i = 1; i <= n; i++)
{
if (m.ContainsKey(i))
{
m[i] = 1;
}
else
{
m.Add(i, 1);
}
}
for(int i = 0; i < v.Count; i++)
{
// Erase exisitng numbers
if (v[i] != -1)
m.Remove(v[i]);
}
// Store non-exisiting
// even and odd numbers
foreach(KeyValuePair i in m)
{
if (i.Key % 2 == 0)
{
even.Add(i.Key);
}
else
{
odd.Add(i.Key);
}
}
min = 1000;
parity(even, odd, v, 0);
Console.WriteLine(min);
}
// Driver Code
static void Main()
{
int n = 8;
List v = new List();
v.Add(2);
v.Add(1);
v.Add(4);
v.Add(-1);
v.Add(-1);
v.Add(6);
v.Add(-1);
v.Add(8);
minDiffParity(v, n);
}
}
// This code is contributed by divyesh072019 输出：
6