public int numberOfArithmeticSlices(int[] nums) {

int l = nums.length;

if (l < 3)

return 0;

int count = 1;

int answer = 0;

int diff = nums[1] - nums[0];

for (int i = 1; i < l; i++) {

if ((nums[i] - nums[i-1]) == diff)

count += 1;

else {

if (count >= 3)

answer += ((count-2) * (count-1)) / 2;

//System.out.println(answer + " - " + count + " - " + nums[i]);

count = 2;

diff = nums[i] - nums[i-1];

}

}

if (count >= 3) {

answer += ((count-2) * (count-1)) / 2;

}

return answer;

}

public int numberOfArithmeticSlices(int[] nums) {

HashMap<Integer,HashSet<Integer>> hm=new HashMap<>();

for(int i=0;i<nums.length;i++){

if(!hm.containsKey(nums[i])){

HashSet<Integer> hs=new HashSet<>();

hs.add(i);

hm.put(nums[i],hs);

}else{

hm.get(nums[i]).add(i);

}

}

int c=0;

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

int d=nums[i]-nums[i-1];

int k=2;

while(i-k>=0&&hm.containsKey(nums[i]-(k*d))&&hm.get(nums[i]-(k*d)).contains(i-k)){

c++;

k++;

}

}

return c;

}

// TC : O(n)

// SC : O(n)

public int numberOfArithmeticSlices(int[] A) {

int[] dp = new int[A.length];

int total = 0;

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

// Third- Second == Second-First

if(A[i] - A[i-1] == A[i-1] - A[i-2]){

dp[i] = dp[i-1]+1;

} else{

dp[i] = 0;

}

total += dp[i];

}

return total;

}

// TC: O(n)

// SC: O(1)

public int numberOfArithmeticSlices(int[] A) {

int previousCount = 0;

int total = 0;

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

if(A[i] - A[i-1] == A[i-1] - A[i-2]){

previousCount = previousCount +1;

} else{

previousCount = 0;

}

total += previousCount;

}

return total;

}

}