在由前 M 个自然数组成的大小为 N 的数组中查找重复元素
给定一个大小为N的数组arr[] ,其中包含从1 到 M的数字排列,以及一个重复的元素(一次或多次),任务是找到重复的元素。
例子:
Input: arr[]={2, 6, 4, 3, 1, 5, 2}, N=7
Output:
2
Explanation: In arr[], all elements from 0 to 6 occurs once, except 2 which is repeated once.
Input: arr[]={2, 1, 3, 1, 1, 1}, N=6
Output:
1
天真的方法:天真的方法是对数组进行排序并检查相邻元素是否相等。
时间复杂度: O(NlogN)
辅助空间: O(1)
解决方法:按照以下步骤解决问题:
- 初始化两个变量M和sum分别存储数组的最大元素和总和。
- 遍历数组arr并执行以下操作:
- 将当前元素加到sum
- 将当前元素与M进行比较以计算最大元素。
- 使用以下公式将从1 到 M的排列总和存储在变量sum1中:
Sum of elements from 1 to X= X*(X+1)/2
- 将答案计算为sum和sum1之间的差除以额外字符的数量,即(sum-sum1)/(NM) 。
下面是上述方法的实现:
C++
// C++ program for the above approach
#include
using namespace std;
// Function to calculate the repeating character in a given
// permutation
int repeatingElement(int arr[], int N)
{
// variables to store maximum element and sum of the
// array respectively.
int M = 0, sum = 0;
for (int i = 0; i < N; i++) {
// calculate sum of array
sum += arr[i];
// calculate maximum element in the array
M = max(M, arr[i]);
}
// calculating sum of permutation
int sum1 = M * (M + 1) / 2;
// calculate required answer
int ans = (sum - sum1) / (N - M);
return ans;
}
// Driver code
int main()
{
// Input
int arr[] = { 2, 6, 4, 3, 1, 5, 2 };
int N = sizeof(arr) / sizeof(arr[0]);
// Function call
cout << repeatingElement(arr, N) << endl;
return 0;
}
Java
// Java Program for the above approach
import java.io.*;
class GFG
{
// Function to calculate the repeating character in a given
// permutation
public static int repeatingElement(int arr[], int N)
{
// variables to store maximum element and sum of the
// array respectively.
int M = 0, sum = 0;
for (int i = 0; i < N; i++) {
// calculate sum of array
sum += arr[i];
// calculate maximum element in the array
M = Math.max(M, arr[i]);
}
// calculating sum of permutation
int sum1 = M * (M + 1) / 2;
// calculate required answer
int ans = (sum - sum1) / (N - M);
return ans;
}
// Driver code
public static void main (String[] args)
{
// Input
int arr[] = { 2, 6, 4, 3, 1, 5, 2 };
int N = arr.length;
// Function call
System.out.println(repeatingElement(arr, N));
}
}
// This code is contributed by lokeshpotta20
Python3
# Python 3 program for the above approach
# Function to calculate the repeating character in a given
# permutation
def repeatingElement(arr, N):
# variables to store maximum element and sum of the
# array respectively.
M = 0
sum = 0
for i in range(N):
# calculate sum of array
sum += arr[i]
# calculate maximum element in the array
M = max(M, arr[i])
# calculating sum of permutation
sum1 = M * (M + 1) // 2
# calculate required answer
ans = (sum - sum1) // (N - M)
return ans
# Driver code
if __name__ == '__main__':
# Input
arr = [2, 6, 4, 3, 1, 5, 2]
N = len(arr)
# Function call
print(repeatingElement(arr, N))
# This code is contributed by SURENDRA_GANGWAR.
C#
// C++ program for the above approach
using System;
// Function to calculate the repeating character in a given
// permutation
public class GFG
{
public static int repeatingElement(int[] arr, int N)
{
// variables to store maximum element and sum of the
// array respectively.
int M = 0, sum = 0;
for (int i = 0; i < N; i++) {
// calculate sum of array
sum += arr[i];
// calculate maximum element in the array
M = Math.Max(M, arr[i]);
}
// calculating sum of permutation
int sum1 = M * (M + 1) / 2;
// calculate required answer
int ans = (sum - sum1) / (N - M);
return ans;
}
// Driver code
public static void Main()
{
// Input
int[] arr = { 2, 6, 4, 3, 1, 5, 2 };
int N = 7;
// Function call
Console.WriteLine(repeatingElement(arr, N));
}
}
// This code is contributed by Sohom Das
Javascript
// JavaScript program for the above approach
// Function to calculate the repeating character in a given
// permutation
function repeatingElement(arr, N)
{
// variables to store maximum element and sum of the
// array respectively.
let M = 0, sum = 0;
for (let i = 0; i < N; i++) {
// calculate sum of array
sum += arr[i];
// calculate maximum element in the array
M = Math.max(M, arr[i]);
}
// calculating sum of permutation
let sum1 = parseInt(M * (M + 1) / 2);
// calculate required answer
let ans = parseInt((sum - sum1) / (N - M));
return ans;
}
// Driver code
// Input
let arr = [2, 6, 4, 3, 1, 5, 2];
let N = arr.length;
// Function call
document.write(repeatingElement(arr, N));
// This code is contributed by Potta Lokesh
输出
2
时间复杂度: O(N)
辅助空间: O(1)