package me.ramswaroop.arrays;
/**
* Created by IntelliJ IDEA.
*
* @author: ramswaroop
* @date: 9/1/15
* @time: 10:21 PM
*/
public class MaxIndexDiff {
/**
* Given an array arr[], find the maximum j – i such that arr[j] > arr[i].
*
* @param a
* @return
*/
public static int maxDiff(int[] a) {
int maxDiff = -1;
int[] leftMin = new int[a.length], rightMax = new int[a.length];
/**
* leftMin[i] holds the smallest element on left side of arr[i] including arr[i].
* In other words, leftMin[i] stores the minimum value from (arr[0], arr[1], ... arr[i]).
*/
leftMin[0] = a[0];
for (int i = 1; i < a.length; i++) {
leftMin[i] = Math.min(a[i], leftMin[i - 1]);
}
/**
* rightMax[i] holds the greatest element on right side of arr[i] including arr[i].
* In other words, rightMax[i] stores the maximum value from (arr[i], arr[i+1], ..arr[n-1])
*/
rightMax[a.length - 1] = a[a.length - 1];
for (int i = a.length - 2; i >= 0; i--) {
rightMax[i] = Math.max(a[i], rightMax[i + 1]);
}
// traverse both arrays from left to right to find maximum j - i
for (int i = 0, j = 0; i < a.length && j < a.length; ) {
if (rightMax[j] > leftMin[i]) {
maxDiff = Math.max(maxDiff, j - i);
j++;
} else {
i++;
}
}
return maxDiff;
}
public static void main(String a[]) {
System.out.println(maxDiff(new int[]{34, 8, 10, 3, 2, 80, 30, 33, 1}));
System.out.println(maxDiff(new int[]{9, 2, 3, 4, 5, 6, 7, 8, 18, 0}));
System.out.println(maxDiff(new int[]{1, 2, 3, 4, 5, 6}));
System.out.println(maxDiff(new int[]{6, 5, 4, 3, 2, 1}));
System.out.println(maxDiff(new int[]{10, 11, 12, 13, 14, 6, 9, 7, 5, 3}));
}
}