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/**
* Is array post order of BST?
* post order: left, right, root
*/
public class IsBSTPostOrder {
public static void main(String[] args) {
int[] a = new int[]{0, 2, 1, 9, 12, 10, 6};
boolean postOrder = isBstPostOrder(a, 0, a.length - 1);
System.out.println(postOrder);
}
public static boolean isBstPostOrder(int[] a, int left, int right) {
if (left > right)
return false;
if ( right == left)
return true;
if(right - left == 1){
return true; //[left, root] or [root, right]
}
int i = left;
for (; i < right; i++) {
if (a[i] > a[right])
break;
}
int j = i;
for (; j < right; j++) {
if (a[j] < a[right])
return false;
}
return isBstPostOrder(a, left, i - 1) && isBstPostOrder(a, i, j-1);
}
}