给定一个大小为N的数组arr[]仅由0 s、 1 s 和2 s 组成，任务是找到包含不同数组元素的索引(i, j, k)三元组的计数，使得i < j < k并且数组元素不是等距的，即(j – i )!= (k – j) 。
例子：
Input: arr[] = { 0, 1, 2, 1 }
Output:1
Explanation:
Only triplet (0, 2, 3) contains distinct array elements and (2 – 0) != (3 – 2).
Therefore, the required output is 1.
Input: arr[] = { 0, 1, 2 }
Output: 0
Explanation:
No triplet exists that satisfy the condition.
Therefore, the required output is 0.
方法：想法是将数组元素0 s、 1 s 和2 s 的索引存储在三个单独的数组中，然后找到满足给定条件的计数三元组。请按照以下步骤解决问题：
- 初始化两个数组，比如zero_i[]和one_i[] ，分别存储给定数组中0和1的索引。
- 初始化一个映射，比如mp ，以存储给定数组中2 s 的索引。
- 通过将zero_i[] 、 one_i[]和mp的大小相乘，求出所有可能的三元组的总数。
- 现在，减去所有违反给定条件的三元组。
- 为了找到这样的三元组，遍历数组zero_i[]和one_i[]并尝试在 Map 中找到违反条件的第三个索引。
- 为了找到违反条件的第三个索引，出现以下三种情况：
- 第三个索引与两个索引的距离相等，并存在于它们之间。
- 第三个索引与两个索引等距，位于第一个索引的左侧。
- 第三个索引与两个索引等距，位于第二个索引的右侧。
- 从三元组总数中删除所有这些三元组。
- 最后，打印获得的三元组的总数。
下面是上述方法的实现：
C++14
// C++ program to implement
// the above approach
#include
using namespace std;
// Function to find the total count of
// triplets (i, j, k) such that i < j < k
// and (j - i) != (k - j)
int countTriplets(int* arr, int N)
{
// Stores indices of 0s
vector zero_i;
// Stores indices of 1s
vector one_i;
// Stores indices of 2s
unordered_map mp;
// Traverse the array
for (int i = 0; i < N; i++) {
// If current array element
// is 0
if (arr[i] == 0)
zero_i.push_back(i + 1);
// If current array element is 1
else if (arr[i] == 1)
one_i.push_back(i + 1);
// If current array element
// is 2
else
mp[i + 1] = 1;
}
// Total count of triplets
int total = zero_i.size()
* one_i.size() * mp.size();
// Traverse the array zero_i[]
for (int i = 0; i < zero_i.size();
i++) {
// Traverse the array one_i[]
for (int j = 0; j < one_i.size();
j++) {
// Stores index of 0s
int p = zero_i[i];
// Stores index of 1s
int q = one_i[j];
// Stores third element of
// triplets that does not
// satisfy the condition
int r = 2 * p - q;
// If r present
// in the map
if (mp[r] > 0)
total--;
// Update r
r = 2 * q - p;
// If r present
// in the map
if (mp[r] > 0)
total--;
// Update r
r = (p + q) / 2;
// If r present in the map
// and equidistant
if (mp[r] > 0 && abs(r - p) == abs(r - q))
total--;
}
}
// Print the obtained count
cout << total;
}
// Driver Code
int main()
{
int arr[] = { 0, 1, 2, 1 };
int N = sizeof(arr) / sizeof(arr[0]);
countTriplets(arr, N);
return 0;
} Java
// Java program to implement
// the above approach
import java.util.*;
class GFG{
// Function to find the total count of
// triplets (i, j, k) such that i < j < k
// and (j - i) != (k - j)
static void countTriplets(int []arr, int N)
{
// Stores indices of 0s
Vector zero_i = new Vector();
// Stores indices of 1s
Vector one_i = new Vector();
// Stores indices of 2s
HashMap mp = new HashMap();
// Traverse the array
for(int i = 0; i < N; i++)
{
// If current array element
// is 0
if (arr[i] == 0)
zero_i.add(i + 1);
// If current array element is 1
else if (arr[i] == 1)
one_i.add(i + 1);
// If current array element
// is 2
else
mp.put(i + 1, 1);
}
// Total count of triplets
int total = zero_i.size() *
one_i.size() * mp.size();
// Traverse the array zero_i[]
for(int i = 0; i < zero_i.size(); i++)
{
// Traverse the array one_i[]
for(int j = 0; j < one_i.size(); j++)
{
// Stores index of 0s
int p = zero_i.get(i);
// Stores index of 1s
int q = one_i.get(j);
// Stores third element of
// triplets that does not
// satisfy the condition
int r = 2 * p - q;
// If r present
// in the map
if (mp.containsKey(r) && mp.get(r) > 0)
total--;
// Update r
r = 2 * q - p;
// If r present
// in the map
if (mp.containsKey(r) && mp.get(r) > 0)
total--;
// Update r
r = (p + q) / 2;
// If r present in the map
// and equidistant
if (mp.containsKey(r) &&
mp.get(r) > 0 &&
Math.abs(r - p) == Math.abs(r - q))
total--;
}
}
// Print the obtained count
System.out.print(total);
}
// Driver Code
public static void main(String[] args)
{
int arr[] = { 0, 1, 2, 1 };
int N = arr.length;
countTriplets(arr, N);
}
}
// This code is contributed by 29AjayKumar Python3
# Python3 program to implement
# the above approach
# Function to find the total count of
# triplets (i, j, k) such that i < j < k
# and (j - i) != (k - j)
def countTriplets(arr, N):
# Stores indices of 0s
zero_i = []
# Stores indices of 1s
one_i = []
# Stores indices of 2s
mp = {}
# Traverse the array
for i in range(N):
# If current array element
# is 0
if (arr[i] == 0):
zero_i.append(i + 1)
# If current array element is 1
elif (arr[i] == 1):
one_i.append(i + 1)
# If current array element
# is 2
else:
mp[i + 1] = 1
# Total count of triplets
total = len(zero_i) * len(one_i) * len(mp)
# Traverse the array zero_i[]
for i in range(len(zero_i)):
# Traverse the array one_i[]
for j in range(len(one_i)):
# Stores index of 0s
p = zero_i[i]
# Stores index of 1s
q = one_i[j]
# Stores third element of
# triplets that does not
# satisfy the condition
r = 2 * p - q
# If r present
# in the map
if (r in mp):
total -= 1
# Update r
r = 2 * q - p
# If r present
# in the map
if (r in mp):
total -= 1
# Update r
r = (p + q) // 2
# If r present in the map
# and equidistant
if ((r in mp) and abs(r - p) == abs(r - q)):
total -= 1
# Print the obtained count
print (total)
# Driver Code
if __name__ == '__main__':
arr = [0, 1, 2, 1]
N = len(arr)
countTriplets(arr, N)
# This code is contributed by mohit kumar 29C#
// C# program to implement
// the above approach
using System;
using System.Collections.Generic;
class GFG{
// Function to find the total count of
// triplets (i, j, k) such that i < j < k
// and (j - i) != (k - j)
static void countTriplets(int []arr, int N)
{
// Stores indices of 0s
List zero_i = new List();
// Stores indices of 1s
List one_i = new List();
// Stores indices of 2s
Dictionary mp = new Dictionary();
// Traverse the array
for(int i = 0; i < N; i++)
{
// If current array element
// is 0
if (arr[i] == 0)
zero_i.Add(i + 1);
// If current array element is 1
else if (arr[i] == 1)
one_i.Add(i + 1);
// If current array element
// is 2
else
mp.Add(i + 1, 1);
}
// Total count of triplets
int total = zero_i.Count *
one_i.Count * mp.Count;
// Traverse the array zero_i[]
for(int i = 0; i < zero_i.Count; i++)
{
// Traverse the array one_i[]
for(int j = 0; j < one_i.Count; j++)
{
// Stores index of 0s
int p = zero_i[i];
// Stores index of 1s
int q = one_i[j];
// Stores third element of
// triplets that does not
// satisfy the condition
int r = 2 * p - q;
// If r present
// in the map
if (mp.ContainsKey(r) && mp[r] > 0)
total--;
// Update r
r = 2 * q - p;
// If r present
// in the map
if (mp.ContainsKey(r) && mp[r] > 0)
total--;
// Update r
r = (p + q) / 2;
// If r present in the map
// and equidistant
if (mp.ContainsKey(r) &&
mp[r] > 0 &&
Math.Abs(r - p) == Math.Abs(r - q))
total--;
}
}
// Print the obtained count
Console.Write(total);
}
// Driver Code
public static void Main(String[] args)
{
int []arr = { 0, 1, 2, 1 };
int N = arr.Length;
countTriplets(arr, N);
}
}
// This code contributed by shikhasingrajput 输出：
1时间复杂度： O(N 2 )
辅助空间： O(N)
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