Find the index of first 1 in a sorted array of 0âs and 1âs
Given a sorted array consisting 0âs and 1âs. The problem is to find the index of first â1â in the sorted array. It could be possible that the array consists of only 0âs or only 1âs. If 1âs are not present in the array then print â-1â.
Examples :
Input : arr[] = {0, 0, 0, 0, 0, 0, 1, 1, 1, 1}
Output : 6
Explanation: The index of first 1 in the array is 6.Input : arr[] = {0, 0, 0, 0}
Output : -1
Explanation: 1âs are not present in the array.
Source: Asked in Amazon Interview
Naive Approach: Traverse the array from left to right and return the index of first â1â. If 1âs are not present in the array, then print â-1â
Implementation:
C++
// C++ implementation to find the index of // first '1' in a sorted array of 0's and 1's #include <bits/stdc++.h> using namespace std; // function to find the index of first '1' int indexOfFirstOne( int arr[], int n) { // traverse the array from left to right for ( int i = 0; i < n; i++) // if true, then return i if (arr[i] == 1) return i; // 1's are not present in the array return -1; } // Driver program to test above int main() { int arr[] = { 0, 0, 0, 0, 0, 0, 1, 1, 1, 1 }; int n = sizeof (arr) / sizeof (arr[0]); cout << indexOfFirstOne(arr, n); return 0; } |
Java
// Java program to find the index of // first '1' in a sorted array of 0's and 1's class GFG { // function to find the index of first '1' public static int indexOfFirstOne( int arr[], int n) { // traverse the array from left to right for ( int i = 0 ; i < n; i++) // if true, then return i if (arr[i] == 1 ) return i; // 1's are not present in the array return - 1 ; } /* Driver program to test above function */ public static void main(String[] args) { int arr[] = { 0 , 0 , 0 , 0 , 0 , 0 , 1 , 1 , 1 , 1 }; int n = arr.length; System.out.println(indexOfFirstOne(arr, n)); } } // This code is contributed by Arnav Kr. Mandal. |
Python3
# Python3 implementation to find # the index of first '1' in a # sorted array of 0's and 1's # function to find the index of first '1' def indexOfFirstOne(arr, n): # traverse the array from left to right for i in range ( 0 , n): # if true, then return i if (arr[i] = = 1 ): return i # 1's are not present in the array return - 1 # Driver program to test above arr = [ 0 , 0 , 0 , 0 , 0 , 0 , 1 , 1 , 1 , 1 ] n = len (arr) ans = indexOfFirstOne(arr, n) print (ans) # This code is contributed by saloni1297 |
C#
// C# program to find the index of // first '1' in a sorted array // of 0's and 1's using System; class GFG { // function to find the index of first '1' public static int indexOfFirstOne( int []arr, int n) { // traverse the array from left to right for ( int i = 0; i < n; i++) // if true, then return i if (arr[i] == 1) return i; // 1's are not present in the array return -1; } // Driver program public static void Main() { int []arr = { 0, 0, 0, 0, 0, 0, 1, 1, 1, 1 }; int n = arr.Length; Console.Write(indexOfFirstOne(arr, n)); } } // This code is contributed by Sam007 |
PHP
<?php // PHP implementation to find the index of // first '1' in a sorted array of 0's and 1's // function to find the index of first '1' function indexOfFirstOne( $arr , $n ) { // traverse the array from // left to right for ( $i = 0; $i < $n ; $i ++) // if true, then return i if ( $arr [ $i ] == 1) return $i ; // 1's are not present // in the array return -1; } // Driver Code $arr = array (0, 0, 0, 0, 0, 0, 1, 1, 1, 1); $n = sizeof( $arr ) / sizeof( $arr [0]); echo indexOfFirstOne( $arr , $n ); return 0; // This code is contributed by nitin mittal. ?> |
Javascript
<script> // Javascript implementation to find the index of // first '1' in a sorted array of 0's and 1's // function to find the index of first '1' function indexOfFirstOne(arr, n) { // traverse the array from left to right for (let i = 0; i < n; i++) // if true, then return i if (arr[i] == 1) return i; // 1's are not present in the array return -1; } // Driver program to test above let arr = [ 0, 0, 0, 0, 0, 0, 1, 1, 1, 1 ]; let n = arr.length; document.write(indexOfFirstOne(arr, n)); //This code is contributed by Mayank Tyagi </script> <script> // Javascript implementation to find the index of // first '1' in a sorted array of 0's and 1's // function to find the index of first '1' function indexOfFirstOne(arr, n) { // traverse the array from left to right for (let i = 0; i < n; i++) // if true, then return i if (arr[i] == 1) return i; // 1's are not present in the array return -1; } // Driver program to test above let arr = [ 0, 0, 0, 0, 0, 0, 1, 1, 1, 1 ]; let n = arr.length; document.write(indexOfFirstOne(arr, n)); //This code is contributed by Mayank Tyagi </script> <script> // Javascript implementation to find the index of // first '1' in a sorted array of 0's and 1's // function to find the index of first '1' function indexOfFirstOne(arr, n) { // traverse the array from left to right for (let i = 0; i < n; i++) // if true, then return i if (arr[i] == 1) return i; // 1's are not present in the array return -1; } // Driver program to test above let arr = [ 0, 0, 0, 0, 0, 0, 1, 1, 1, 1 ]; let n = arr.length; document.write(indexOfFirstOne(arr, n)); //This code is contributed by Mayank Tyagi </script> <script> // Javascript implementation to find the index of // first '1' in a sorted array of 0's and 1's // function to find the index of first '1' function indexOfFirstOne(arr, n) { // traverse the array from left to right for (let i = 0; i < n; i++) // if true, then return i if (arr[i] == 1) return i; // 1's are not present in the array return -1; } // Driver program to test above let arr = [ 0, 0, 0, 0, 0, 0, 1, 1, 1, 1 ]; let n = arr.length; document.write(indexOfFirstOne(arr, n)); //This code is contributed by Mayank Tyagi </script> <script> // Javascript implementation to find the index of // first '1' in a sorted array of 0's and 1's // function to find the index of first '1' function indexOfFirstOne(arr, n) { // traverse the array from left to right for (let i = 0; i < n; i++) // if true, then return i if (arr[i] == 1) return i; // 1's are not present in the array return -1; } // Driver program to test above let arr = [ 0, 0, 0, 0, 0, 0, 1, 1, 1, 1 ]; let n = arr.length; document.write(indexOfFirstOne(arr, n)); //This code is contributed by Mayank Tyagi </script> <script> // Javascript implementation to find the index of // first '1' in a sorted array of 0's and 1's // function to find the index of first '1' function indexOfFirstOne(arr, n) { // traverse the array from left to right for (let i = 0; i < n; i++) // if true, then return i if (arr[i] == 1) return i; // 1's are not present in the array return -1; } // Driver program to test above let arr = [ 0, 0, 0, 0, 0, 0, 1, 1, 1, 1 ]; let n = arr.length; document.write(indexOfFirstOne(arr, n)); //This code is contributed by Mayank Tyagi </script> <script> // Javascript implementation to find the index of // first '1' in a sorted array of 0's and 1's // function to find the index of first '1' function indexOfFirstOne(arr, n) { // traverse the array from left to right for (let i = 0; i < n; i++) // if true, then return i if (arr[i] == 1) return i; // 1's are not present in the array return -1; } // Driver program to test above let arr = [ 0, 0, 0, 0, 0, 0, 1, 1, 1, 1 ]; let n = arr.length; document.write(indexOfFirstOne(arr, n)); //This code is contributed by Mayank Tyagi </script> <script> // Javascript implementation to find the index of // first '1' in a sorted array of 0's and 1's // function to find the index of first '1' function indexOfFirstOne(arr, n) { // traverse the array from left to right for (let i = 0; i < n; i++) // if true, then return i if (arr[i] == 1) return i; // 1's are not present in the array return -1; } // Driver program to test above let arr = [ 0, 0, 0, 0, 0, 0, 1, 1, 1, 1 ]; let n = arr.length; document.write(indexOfFirstOne(arr, n)); //This code is contributed by Mayank Tyagi </script> <script> // Javascript implementation to find the index of // first '1' in a sorted array of 0's and 1's // function to find the index of first '1' function indexOfFirstOne(arr, n) { // traverse the array from left to right for (let i = 0; i < n; i++) // if true, then return i if (arr[i] == 1) return i; // 1's are not present in the array return -1; } // Driver program to test above let arr = [ 0, 0, 0, 0, 0, 0, 1, 1, 1, 1 ]; let n = arr.length; document.write(indexOfFirstOne(arr, n)); //This code is contributed by Mayank Tyagi </script> <script> // Javascript implementation to find the index of // first '1' in a sorted array of 0's and 1's // function to find the index of first '1' function indexOfFirstOne(arr, n) { // traverse the array from left to right for (let i = 0; i < n; i++) // if true, then return i if (arr[i] == 1) return i; // 1's are not present in the array return -1; } // Driver program to test above let arr = [ 0, 0, 0, 0, 0, 0, 1, 1, 1, 1 ]; let n = arr.length; document.write(indexOfFirstOne(arr, n)); //This code is contributed by Mayank Tyagi </script> |
6
Time Complexity: O(n)
Auxiliary Space: O(1)
Efficient Approach(Binary Search): Use the technique of binary search on the sorted array, so as to find the index of first â1â.
Implementation:
C++
// C++ implementation to find the index of first // '1' in a sorted array of 0's and 1's #include <bits/stdc++.h> using namespace std; // function to find the index of first '1' // binary search technique is applied int indexOfFirstOne( int arr[], int low, int high) { while (low <= high) { int mid = (low + high) / 2; // if true, then 'mid' is the index of first '1' if (arr[mid] == 1 && (mid == 0 || arr[mid - 1] == 0)) return mid; // first '1' lies to the left of 'mid' else if (arr[mid] == 1) high = mid - 1; // first '1' lies to the right of 'mid' else low = mid + 1; } // 1's are not present in the array return -1; } // Driver program to test above int main() { int arr[] = { 0, 0, 0, 0, 0, 0, 1, 1, 1, 1 }; int n = sizeof (arr) / sizeof (arr[0]); cout << indexOfFirstOne(arr, 0, n - 1); return 0; } |
Java
// Java program to find the index of // first '1' in a sorted array of 0's and 1's class GFG { // function to find the index of first '1' // binary search technique is applied public static int indexOfFirstOne( int arr[], int low, int high) { while (low <= high) { int mid = (low + high) / 2 ; // if true, then 'mid' is the index of first '1' if (arr[mid] == 1 && (mid == 0 || arr[mid - 1 ] == 0 )) return mid; // first '1' lies to the left of 'mid' else if (arr[mid] == 1 ) high = mid - 1 ; // first '1' lies to the right of 'mid' else low = mid + 1 ; } // 1's are not present in the array return - 1 ; } /* Driver program to test above function */ public static void main(String[] args) { int arr[] = { 0 , 0 , 0 , 0 , 0 , 0 , 1 , 1 , 1 , 1 }; int n = arr.length; System.out.println(indexOfFirstOne(arr, 0 , n - 1 )); } } // This code is contributed by Arnav Kr. Mandal. |
Python3
# Python3 implementation to find # the index of first '1' in a # sorted array of 0's and 1's # function to find the index of first '1' # binary search technique is applied def indexOfFirstOne( arr, low, high): while (low < = high): mid = int ((low + high) / 2 ) # if true, then 'mid' is the index of first '1' if (arr[mid] = = 1 and (mid = = 0 or arr[mid - 1 ] = = 0 )): return mid # first '1' lies to the left of 'mid' elif (arr[mid] = = 1 ): high = mid - 1 # first '1' lies to the right of 'mid' else : low = mid + 1 # 1's are not present in the array return - 1 ; # Driver program to test above arr = [ 0 , 0 , 0 , 0 , 0 , 0 , 1 , 1 , 1 , 1 ] n = len (arr) ans = indexOfFirstOne(arr, 0 , n - 1 ) print (ans) # This code is contributed by saloni1297 |
C#
// C# program to find the index of // first '1' in a sorted array of 0's and 1's using System; class GFG { // function to find the index of first '1' // binary search technique is applied public static int indexOfFirstOne( int []arr, int low, int high) { while (low <= high) { int mid = (low + high) / 2; // if true, then 'mid' is the index of first '1' if (arr[mid] == 1 && (mid == 0 || arr[mid - 1] == 0)) return mid; // first '1' lies to the left of 'mid' else if (arr[mid] == 1) high = mid - 1; // first '1' lies to the right of 'mid' else low = mid + 1; } // 1's are not present in the array return -1; } // Driver program public static void Main() { int []arr = { 0, 0, 0, 0, 0, 0, 1, 1, 1, 1 }; int n = arr.Length; Console.Write(indexOfFirstOne(arr, 0, n - 1)); } } // This code is contributed by Sam007 |
PHP
<?php // PHP implementation to find // the index of first '1' in // a sorted array of 0's and 1's // function to find the index // of first '1' binary search // technique is applied function indexOfFirstOne( $arr , $low , $high ) { while ( $low <= $high ) { $mid = ceil ( $low + $high ) / 2; // if true, then 'mid' is // the index of first '1' if ( $arr [ $mid ] == 1 and ( $mid == 0 or $arr [ $mid - 1] == 0)) return $mid ; // first '1' lies to the // left of 'mid' else if ( $arr [ $mid ] == 1) $high = $mid - 1; // first '1' lies to // the right of 'mid' else $low = $mid + 1; } // 1's are not present // in the array return -1; } // Driver Code $arr = array (0, 0, 0, 0, 0, 0, 1, 1, 1, 1); $n = count ( $arr ); echo indexOfFirstOne( $arr , 0, $n - 1); // This code is contributed by anuj_67. ?> |
Javascript
<script> // Javascript implementation to find the index of first // '1' in a sorted array of 0's and 1's // function to find the index of first '1' // binary search technique is applied function indexOfFirstOne(arr, low, high) { while (low <= high) { var mid = parseInt((low + high) / 2); // if true, then 'mid' is the index of first '1' if (arr[mid] == 1 && (mid == 0 || arr[mid - 1] == 0)) return mid; // first '1' lies to the left of 'mid' else if (arr[mid] == 1) high = mid - 1; // first '1' lies to the right of 'mid' else low = mid + 1; } // 1's are not present in the array return -1; } // Driver program to test above var arr = [0, 0, 0, 0, 0, 0, 1, 1, 1, 1]; var n = arr.length; document.write( indexOfFirstOne(arr, 0, n - 1)); // This code is contributed by rrrtnx. </script> |
6
Time Complexity: O(Logn)
Auxiliary Space: O(1)