<p>Given a binary array <code>nums</code> and an integer <code>goal</code>, return <em>the number of non-empty <strong>subarrays</strong> with a sum</em> <code>goal</code>.</p>

<p>A <strong>subarray</strong> is a contiguous part of the array.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

<pre>
<strong>Input:</strong> nums = [1,0,1,0,1], goal = 2
<strong>Output:</strong> 4
<strong>Explanation:</strong> The 4 subarrays are bolded and underlined below:
[<u><strong>1,0,1</strong></u>,0,1]
[<u><strong>1,0,1,0</strong></u>,1]
[1,<u><strong>0,1,0,1</strong></u>]
[1,0,<u><strong>1,0,1</strong></u>]
</pre>

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> nums = [0,0,0,0,0], goal = 0
<strong>Output:</strong> 15
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>1 &lt;= nums.length &lt;= 3 * 10<sup>4</sup></code></li>
	<li><code>nums[i]</code> is either <code>0</code> or <code>1</code>.</li>
	<li><code>0 &lt;= goal &lt;= nums.length</code></li>
</ul>

class Solution {
public:
    int numSubarraysWithSum(vector<int>& nums, int goal) {
        if(goal == 0 && accumulate(nums.begin() , nums.end() , 0) == 0)
        {
            int n = nums.size();
            return (n*(n+1))/2;
        }
        else if(goal == 0 && accumulate(nums.begin() , nums.end() , 0)!=0)
        {
            int left = 0;
            int right = 0;
            int count = 0;
            int sum = 0;

            while(right < nums.size())
            {
                if(nums[right] == 1)
                {
                    count += (sum*(sum+1))/2;
                    left = right+1;
                    sum = 0;
                }
                else
                {
                    sum++;
                }
                if(right == nums.size() - 1)
                {
                    count += (sum*(sum+1))/2;
                }
                right++;
            }

            return count;
        }
        else
        {
            int left = 0;
            int right = 0;
            int count = 0;
            int sum = 0;
            vector<int> vec;

            while(right < nums.size())
            {
                sum+=nums[right];
                if(nums[right] == 1)
                {
                    vec.push_back(right);
                }
                if(sum == goal)
                {
                    count+=vec[0] - left +1;
                    right++;
                    while(right < nums.size() && nums[right]!=1)
                    {
                        count+=vec[0] - left +1;
                        right++;
                    }
                    left = vec[0]+1;
                    vec.erase(vec.begin());
                    sum--;
                }
                else
                {
                right++;
                }
            }

            return count;
        }
        
        

    }
};
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