text: // Given an array, find the nearest smaller element G[i] for every element A[i] in the array such that the element has an index smaller than i.
  
  // More formally,
  
  //     G[i] for an element A[i] = an element A[j] such that 
  //     j is maximum possible AND 
  //     j < i AND
  //     A[j] < A[i]
  // Elements for which no smaller element exist, consider next smaller element as -1.
  
  // Input Format
  
  // The only argument given is integer array A.
  // Output Format
  
  // Return the integar array G such that G[i] contains nearest smaller number than A[i].If no such element occurs G[i] should be -1.
  // For Example
  
  // Input 1:
  //     A = [4, 5, 2, 10, 8]
  // Output 1:
  //     G = [-1, 4, -1, 2, 2]
  // Explaination 1:
  //     index 1: No element less than 4 in left of 4, G[1] = -1
  //     index 2: A[1] is only element less than A[2], G[2] = A[1]
  //     index 3: No element less than 2 in left of 2, G[3] = -1
  //     index 4: A[3] is nearest element which is less than A[4], G[4] = A[3]
  //     index 4: A[3] is nearest element which is less than A[5], G[5] = A[3]
  
  vector<int> Solution::prevSmaller(vector<int> &a) {
      int n=a.size();
      vector<int> ans(n,-1);
      stack<int>st;
      for(int i=0;i<n;i++)
      {
          while(!st.empty() && st.top()>=a[i]) st.pop();
          if(!st.empty()) ans[i]=st.top();
          st.push(a[i]);
      }
      return ans;
  }
  