到每个数组索引的最小缺失非负整数

给定一个大小为N的数组arr[] ，任务是为每个数组索引找到最小的缺失非负整数，直到给定数组的该索引。

例子：

Input: arr[] = {1, 3, 0, 2}
Output: 0 0 2 4
Explanation:
Smallest missing non-negative integer from index 0 to 0 is 0.
Smallest missing non-negative integer from index 0 to 1 is 0.
Smallest missing non-negative integer from index 0 to 2 is 2.
Smallest missing non-negative integer from index 0 to 3 is 4.

Input: arr[] = {0, 1, 2, 3, 5}
Output: 1 2 3 4 4

方法：这个问题可以使用Hashing来解决。请按照以下步骤解决问题：

• 初始化一个变量，比如smNonNeg来存储给定数组的起始索引和当前索引之间的最小缺失非负整数。
• 初始化一个数组，比如hash[N]来检查smNonNeg 是否存在于起始索引和当前索引之间。
• 遍历给定的数组并检查hash[smNonNeg] 是否等于0 。如果发现为真，则打印smNonNeg的值。
• 否则，当hash[smNonNeg]不等于0 时，增加smNonNeg的值。

下面是上述方法的实现：

C++

// C++ program to implement
// the above approach
 
#include 
using namespace std;
 
// Function to print the smallest
// missing non-negative integer
// up to every array indices
void smlstNonNeg(int arr[], int N)
{
    // Stores the smallest missing
    // non-negative integers between
    // start index to current index
    int smNonNeg = 0;
 
    // Store the boolean value to check
    // smNonNeg present between start
    // index to each index of the array
    bool hash[N + 1] = { 0 };
 
    // Traverse the array
    for (int i = 0; i < N; i++) {
 
        // Since output always lies
        // in the range[0, N - 1]
        if (arr[i] >= 0 and arr[i] < N) {
            hash[arr[i]] = true;
        }
 
        // Check if smNonNeg is
        // present between start index
        // and current index or not
        while (hash[smNonNeg]) {
            smNonNeg++;
        }
 
        // Print smallest missing
        // non-negative integer
        cout << smNonNeg << " ";
    }
}
 
// Driver Code
int main()
{
    int arr[] = { 0, 1, 2, 3, 5 };
    int N = sizeof(arr) / sizeof(arr[0]);
    smlstNonNeg(arr, N);
}

Java

// Java program to implement
// the above approach
import java.io.*;
import java.util.Arrays;
 
class GFG{
  
// Function to print the smallest
// missing non-negative integer
// up to every array indices
static void smlstNonNeg(int arr[], int N)
{
     
    // Stores the smallest missing
    // non-negative integers between
    // start index to current index
    int smNonNeg = 0;
  
    // Store the boolean value to check
    // smNonNeg present between start
    // index to each index of the array
    Boolean[] hash = new Boolean[N + 1];
    Arrays.fill(hash, false);
 
    // Traverse the array
    for(int i = 0; i < N; i++)
    {
         
        // Since output always lies
        // in the range[0, N - 1]
        if (arr[i] >= 0 && arr[i] < N)
        {
            hash[arr[i]] = true;
        }
  
        // Check if smNonNeg is
        // present between start index
        // and current index or not
        while (hash[smNonNeg])
        {
            smNonNeg++;
        }
  
        // Print smallest missing
        // non-negative integer
        System.out.print(smNonNeg + " ");
    }
}
  
// Driver Code
public static void main (String[] args)
{
    int arr[] = { 0, 1, 2, 3, 5 };
    int N = arr.length;
     
    smlstNonNeg(arr, N);
}
}
 
// This code is contributed by sanjoy_62

Python3

# Python3 program to implement
# the above approach
 
# Function to prthe smallest
# missing non-negative integer
# up to every array indices
def smlstNonNeg(arr, N):
     
    # Stores the smallest missing
    # non-negative integers between
    # start index to current index
    smNonNeg = 0
 
    # Store the boolean value to check
    # smNonNeg present between start
    # index to each index of the array
    hash = [0] * (N + 1)
 
    # Traverse the array
    for i in range(N):
 
        # Since output always lies
        # in the range[0, N - 1]
        if (arr[i] >= 0 and arr[i] < N):
            hash[arr[i]] = True
 
        # Check if smNonNeg is
        # present between start index
        # and current index or not
        while (hash[smNonNeg]):
            smNonNeg += 1
 
        # Print smallest missing
        # non-negative integer
        print(smNonNeg, end = " ")
 
# Driver Code
if __name__ == '__main__':
     
    arr = [ 0, 1, 2, 3, 5 ]
    N = len(arr)
     
    smlstNonNeg(arr, N)
 
# This code is contributed by mohit kumar 29

C#

// C# program to implement
// the above approach
using System;
  
class GFG{
   
// Function to print the smallest
// missing non-negative integer
// up to every array indices
static void smlstNonNeg(int[] arr, int N)
{
     
    // Stores the smallest missing
    // non-negative integers between
    // start index to current index
    int smNonNeg = 0;
   
    // Store the boolean value to check
    // smNonNeg present between start
    // index to each index of the array
    bool[] hash = new bool[N + 1];
     
    for(int i = 0; i < N; i++)
    {
        hash[i] = false;
    }
     
    // Traverse the array
    for(int i = 0; i < N; i++)
    {
         
        // Since output always lies
        // in the range[0, N - 1]
        if (arr[i] >= 0 && arr[i] < N)
        {
            hash[arr[i]] = true;
        }
   
        // Check if smNonNeg is
        // present between start index
        // and current index or not
        while (hash[smNonNeg])
        {
            smNonNeg++;
        }
   
        // Print smallest missing
        // non-negative integer
        Console.Write(smNonNeg + " ");
    }
}
   
// Driver Code
public static void Main ()
{
    int[] arr = { 0, 1, 2, 3, 5 };
    int N = arr.Length;
      
    smlstNonNeg(arr, N);
}
}
 
// This code is contributed by code_hunt

Javascript

 
// Javascript program to implement
// the above approach
 
// Function to prlet the smallest
// missing non-negative leteger
// up to every array indices
function smlstNonNeg(arr, N)
{
     
    // Stores the smallest missing
    // non-negative letegers between
    // start index to current index
    let smNonNeg = 0;
    
    // Store the boolean value to check
    // smNonNeg present between start
    // index to each index of the array
    let hash = [];
      
    for(let i = 0; i < N; i++)
    {
        hash[i] = false;
    }
      
    // Traverse the array
    for(let i = 0; i < N; i++)
    {
          
        // Since output always lies
        // in the range[0, N - 1]
        if (arr[i] >= 0 && arr[i] < N)
        {
            hash[arr[i]] = true;
        }
    
        // Check if smNonNeg is
        // present between start index
        // and current index or not
        while (hash[smNonNeg])
        {
            smNonNeg++;
        }
    
        // Prlet smallest missing
        // non-negative leteger
        document.write(smNonNeg + " ");
    }
}
 
// Driver Code
let arr = [ 0, 1, 2, 3, 5 ];
let N = arr.length;
   
smlstNonNeg(arr, N);
 
// This code is contributed by target_2   
 

输出：

1 2 3 4 4

时间复杂度： O(N)
辅助空间： O(N)

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