lec6_16.cpp

vector<int> nextSmallerElement(vector<int> &arr, int n)
{
    // Write your code here.
    vector<int>ans(n, -1);
    stack <int> st;

    for(int i = 0 ;i<n;i++)
    {
        while(!st.empty() && arr[i] < arr[st.top()])
        {
            ans[st.top()] = arr[i];
            st.top();
        }

        st.push(i);
    }

    return ans;
}