Find local minima in an array

Question

Given an array of integers, find the local minima. An element A[i] is defined as a local minimum if A[i-1] > A[i] and A[i] < A[i+1] where i = 1...n-2. In case of boundar

Answer 1

Here is a solution that works on O(log n). Basically, this works on the merge sort approach (divide and conquer).

public class LocalMaxima {
    int []a = {5,8,10,25,6,3,44,51,55,56,57,58,34,5,59};

    @Test 
    public  void localMaxima () {
        System.out.println((a[localMaxima(0,a.length-1)]));
    }

    int localMaxima(int low, int high) {
        if(high-low > 2) {
            int mid = (low+high)/2;
            return maxof(localMaxima(low,mid),localMaxima(mid+1, high));
        }
        else if(high-low == 1) {
            return maxof(high,low);
        }
        else if(high-low == 0) {
            return high;
        }
        if(high-low == 2) {
            return maxof(maxof(low, high),low+1);
        }
        return 0;
    }

    int maxof(int i, int j) {
        if(a[i]