<p>Given an integer array <code>nums</code> and an integer <code>k</code>, return <em>the length of the shortest non-empty <strong>subarray</strong> of </em><code>nums</code><em> with a sum of at least </em><code>k</code>. If there is no such <strong>subarray</strong>, return <code>-1</code>.</p>

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

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>
<pre><strong>Input:</strong> nums = [1], k = 1
<strong>Output:</strong> 1
</pre><p><strong class="example">Example 2:</strong></p>
<pre><strong>Input:</strong> nums = [1,2], k = 4
<strong>Output:</strong> -1
</pre><p><strong class="example">Example 3:</strong></p>
<pre><strong>Input:</strong> nums = [2,-1,2], k = 3
<strong>Output:</strong> 3
</pre>
<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>1 &lt;= nums.length &lt;= 10<sup>5</sup></code></li>
	<li><code>-10<sup>5</sup> &lt;= nums[i] &lt;= 10<sup>5</sup></code></li>
	<li><code>1 &lt;= k &lt;= 10<sup>9</sup></code></li>
</ul>

class Solution {
public:

typedef long int li;
typedef pair<li,li> pi;

    int shortestSubarray(vector<int>& nums, int k) 
    {
        int n = nums.size();

        priority_queue <pi,vector<pi>,greater<pi>> pq;
        vector <li> subarraySum;

        for(auto x:nums)
        {
            subarraySum.push_back((li)x);
        }

        // if single element is satisfying the condition, min subarray size is 1.
        //
        if(nums[0]>=k)
        return 1;

        int res = INT_MAX;

        pq.push({subarraySum[0],0});

        for(int i=1; i<n; i++)
        {
            subarraySum[i] += subarraySum[i-1];

            if(subarraySum[i] >= k)
            {
                res = min(res,i+1);
            }

            while(!pq.empty() && ( subarraySum[i] - pq.top().first) >= k)
            {
                res = min(res,i-(int)pq.top().second);
                pq.pop();
            }
            pq.push({subarraySum[i],i});
        }
        
        if(res==INT_MAX)
        return -1;

        return res;
    }
};
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