public static void main (String[] args) {

System.out.println(isSystematicallyIncreasing(new int[] {}));

System.out.println(isSystematicallyIncreasing(new int[] {1}));

System.out.println(isSystematicallyIncreasing(new int[] {1, 1}));

System.out.println(isSystematicallyIncreasing(new int[] {1, 2}));

System.out.println(isSystematicallyIncreasing(new int[] {1, 2, 1, 2, 3}));

System.out.println(isSystematicallyIncreasing(new int[] {1, 1, 3}));

System.out.println(isSystematicallyIncreasing(new int[] {1, 2, 1, 2, 1, 2}));

System.out.println(isSystematicallyIncreasing(new int[] {1, 2, 3, 1, 2, 1}));

System.out.println(isSystematicallyIncreasing(new int[] {1, 1, 2, 3}));

System.out.println(isSystematicallyIncreasing(new int[] {1, 1, 2, 1, 2, 3, 1, 2, 3, 4}));

System.out.println(isSystematicallyIncreasing(new int[] {1, 1, 2, 1, 2, 3, 1, 2, 3}));

System.out.println(isSystematicallyIncreasing(new int[] {1, 1, 2, 1, 2, 3}));

System.out.println(isSystematicallyIncreasing(new int[] {1, 1, 2, 1, 2, 3, 1, 2, 3, 4, 1, 2, 3, 4, 5}));

System.out.println(isSystematicallyIncreasing(new int[] {1, 1, 2, 1, 2, 3, 1, 2, 3, 4, 1, 2, 3}));

System.out.println(isSystematicallyIncreasing(new int[] {1, 1, 2}));

System.out.println(isSystematicallyIncreasing(new int[] {1, 1, 2, 1, 2, 3, 1, 2, 3, 4, 1, 2, 3, 4, 5, 1, 2, 3, 4, 5, 6}));

System.out.println(isSystematicallyIncreasing(new int[] {1, 1, 2, 1, 2, 3, 1, 2, 3, 4, 1, 2, 3, 5, 1, 2, 3, 4, 5, 6}));

}

static int isSystematicallyIncreasing (int[] a) {

if (a == null || a.length == 0) return 0;

// if first element is not 1 or length is 2 (Eg. {1, 1})

if (a[0] != 1 || a.length == 2) return 0;

int startIndex = 1;

int j;

// start an outer loop so that inner loop can test for values

for (int i = 2; i < a.length; i++) {

// to remove array with incomplete digits (Coz length needs to be 1, 3, 6, 10, 15 and so on)

if (a.length < i + startIndex) {

return 0;

}

// test for values using inner loop

int num = 1;

for (j = startIndex; j < i + startIndex; j++) {

if (a[j] != num) {

return 0;

}

num ++;

}

// if all digits in the array are tested and none are failing above conditions,

// the array must now be a SystematicallyIncreasing array

if (a.length == i + startIndex) {

break;

}

startIndex = j;

}

return 1;

}