Algorithms and Me: Curious case of Missing and repeating number Part -2

Problem 1 : Given an array of sorted number of size N and contains numbers in range 1 to N-1. Find the smallest missing number.
Binary Search: check whether a[mid] != mid+ 1

Problem 2 : Given an array of size N, find all duplicate numbers. ==> also contains numbers in range 1 to N-1. 

int find_duplicates(int a[], int n){

 

  int i =0;

 

  for(i=0; i<n; i++){

    if(a[abs(a[i])] >0){

      a[abs(a[i])] = - a[abs(a[i])];

    }

    else

      printf("\n %d" , abs(a[i]));

    }

}

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