From 928baa858fd051f3b6ce0f416c67a981843b20a5 Mon Sep 17 00:00:00 2001
From: Samruddhi Ghodake <72791227+samughodake@users.noreply.github.com>
Date: Sat, 25 Sep 2021 03:20:23 +0530
Subject: [PATCH] chore(CPlusPlus): added new array program (#479)

---
 .../occurence-of-one-in-sorted-array.cpp      | 64 +++++++++++++++++++
 algorithms/CPlusPlus/README.md                |  1 +
 2 files changed, 65 insertions(+)
 create mode 100644 algorithms/CPlusPlus/Arrays/occurence-of-one-in-sorted-array.cpp

diff --git a/algorithms/CPlusPlus/Arrays/occurence-of-one-in-sorted-array.cpp b/algorithms/CPlusPlus/Arrays/occurence-of-one-in-sorted-array.cpp
new file mode 100644
index 00000000..6b6e8a7e
--- /dev/null
+++ b/algorithms/CPlusPlus/Arrays/occurence-of-one-in-sorted-array.cpp
@@ -0,0 +1,64 @@
+/*
+Description: Index of first 1 in a sorted array of 0s and 1s.
+Given a sorted array consisting 0’s and 1’s. The task is to find the index of first ‘1’ in the given array.
+
+Approach: Use binary search to solve in least time complexity (O log n).
+*/
+
+#include <iostream>
+#include <algorithm>
+using namespace std;
+ int firstIndex(int a[], int n)  {
+      
+      int low=0;
+      int high=n-1;
+
+      while(low<=high) {
+          int mid = (low+high)/2;
+            //if mid appears to be 0, update low as mid+1 index because we want to search 1 in array
+            if(a[mid]==0){
+                low=mid+1;
+            }
+            //checking if mid element is 1 and the element at mid-1 is 0
+            //if it is so, then we have found index of first 1
+            //simply return mid
+            else if(a[mid]==1 && (mid==0 || a[mid-1]==0)){
+                return mid;
+            }
+            //updating the high to mid-1
+            //because the element at mid-1 index is not zero
+            else if (a[mid]==1){
+                high=mid-1;
+            }
+        }
+        //if index not found, return -1
+        return -1;
+    }
+int main() {
+  int n;
+  cout << "Enter number of elements in an array\n";
+  cin>>n;
+  int a[n];
+  cout<<"Enter array elements: (only 0 and 1 in sorted order)\n";
+  for(int i=0;i<n;i++){
+    cin>>a[i];
+  }
+  //if someone forgets to pass sorted array
+  sort(a,a+n);
+  int ind = firstIndex(a,n);
+  cout<<"Index of first 1 in sorted array: "<<ind;
+}
+
+/*
+Sample Input:
+Enter number of elements in an array
+4
+Enter array elements: (only 0 and 1 in sorted order)
+0
+0
+0
+1
+
+Output:
+Index of first 1 in sorted array: 3
+*/
diff --git a/algorithms/CPlusPlus/README.md b/algorithms/CPlusPlus/README.md
index bd539d77..1b3086fb 100644
--- a/algorithms/CPlusPlus/README.md
+++ b/algorithms/CPlusPlus/README.md
@@ -16,6 +16,7 @@
 12. [Leaders In The Array](Arrays/leaders-in-array.cpp)
 13. [Elements appear thrice In The Array](Arrays/Elements_appears_thrice.cpp)
 14. [Maximum Difference](Arrays/maximum-difference.cpp)
+15. [Occurrence of one in sorted array](algorithms/CPlusPlus/Arrays/occurence-of-one-in-sorted-array.cpp)
 
 ## Dynamic-Programming