NearestGreatestToLeft.cpp

Given an array of integers, find the closest (not considering distance, but value) greater on left of every element. If an element has no greater on the left side, print -1 

int n=arr.size();
stack<int>st;
vector<int> ans;
for(int i=0;i<n;i++){
  if(st.size()==0){
    ans.pb(-1);
  }
  else if(st.size()>0 && st.top()>=arr[i]){
    ans.pb(st.top());
  }
  else if(st.size()>0 && st.top()<arr[i]){
    while(st.size()>0 && st.top()<arr[i])st.pop();
    if(st.size()==0)ans.pb(-1);
    else ans.pb(st.top());
  }
  st.push(arr[i]);
}
//reverse(ans.begin(),ans.end());