Question

Need help to answer this method in java

Write a method

int indexFirstOne(int[ ] input)

The input array is sorted, and every element is 0 or 1. Return the index of the first 1. If there are no 1s in the array, return -1. The worst-case runtime must be O(logn)where n is the number of elements (no credits for slower runtimes)

Example:

a = [0,0,1,1,1]      return 2

a = [ 0,0,0,1]          return 3

a = [0,0,0]              return -1

int indexFirstOne (int [ ] input) {

Answer 1

int indexFirstOne(int[ ] input){

// iterating from both sides
   for(int i=0,j=input.length-1;i<=j;i++,j--){

//if it reaches 1 than return i
       if(input[i]==1){
           return i;
       }

//if it reaches 0, than return j+1
       if(input[j]==0)
           return j+1;
   }
   return -1;
}
}