/****************************************************************************** * Compilation: javac BitonicMax.java * Execution: java BitonicMax N * Dependencies: StdOut.java * * Find the maximum in a bitonic array (strictly increasing, then strictly * decreasing) of size N in log N time. * * % java BitonicMax N * ******************************************************************************/ public class BitonicMax { // create a bitonic array of size N public static int[] bitonic(int N) { int mid = StdRandom.uniformInt(N); int[] a = new int[N]; for (int i = 1; i < mid; i++) { a[i] = a[i-1] + 1 + StdRandom.uniformInt(9); } if (mid > 0) a[mid] = a[mid-1] + StdRandom.uniformInt(10) - 5; for (int i = mid + 1; i < N; i++) { a[i] = a[i-1] - 1 - StdRandom.uniformInt(9); } for (int i = 0; i < N; i++) { StdOut.println(a[i]); } return a; } // find the index of the maximum in a bitonic subarray a[lo..hi] public static int max(int[] a, int lo, int hi) { if (hi == lo) return hi; int mid = lo + (hi - lo) / 2; if (a[mid] < a[mid + 1]) return max(a, mid+1, hi); if (a[mid] > a[mid + 1]) return max(a, lo, mid); else return mid; } public static void main(String[] args) { int N = Integer.parseInt(args[0]); int[] a = bitonic(N); StdOut.println("max = " + a[max(a, 0, N-1)]); } }