<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:
    int shortestSubarray(vector<int>& nums, int k) {
        int n = nums.size();
        map<long long, int> mpp; // save the latest index
        long long preSum = 0;

        int minLen = INT_MAX;
        mpp[0] = -1; // Initialize with 0 sum at index -1

        for(int i = 0; i < n; i++) {
            preSum += nums[i];

            auto it = mpp.upper_bound(preSum - k);
            if(it != mpp.begin()) {
                --it;
                // cout << "WOW " << i << " " << distance(mpp.begin(), it) << endl;
                minLen = min(minLen, i - it->second);
            }
            
            // We remove the preSum from the map which are less than the curr preSum as it gives wrong 
            // results due to negative numbers

            // as soon as -ve num comes prefixSum reduces

            while(!mpp.empty() && mpp.rbegin()->first >= preSum) {
                mpp.erase(prev(mpp.end()));
            }

            mpp[preSum] = i;
        }

        return minLen == INT_MAX ? -1 : minLen;
    }
};
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