LeetCode.1488 Avoid Flood in The City

1.Problem
https://leetcode.com/contest/weekly-contest-194/problems/avoid-flood-in-the-city/

2.Idea
set lower bound

3.Source

 class Solution {  
 public:  
      vector<int> avoidFlood(vector<int>& rains) {  
           int n = rains.size();  
           vector<int> emt, ans;  
           if (n == 0) return emt;  
           set<int> st;  
           map<int, int> mp;  
           ans.resize(n, -1);  
           for (int i = 0; i < n; i++) {  
                if (rains[i] == 0) {  
                     st.insert(i);  
                }  
                else {  
                     int cur = rains[i];  
                     if (mp.find(cur) == mp.end()) {  
                          mp[cur] = i;  
                     }  
                     else {  
                          if (st.size() == 0) return emt;  
                          set<int>::iterator it = st.lower_bound(mp[cur]);  
                          if (it == st.end()) return emt;  
                          else {  
                               ans[*it] = cur;  
                               st.erase(*it);  
                               mp[cur] = i;  
                          }  
                     }  
                }  
           }  
           for (int i = 0; i < n; i++) {  
                if (rains[i] > 0) ans[i] = -1;  
                else if (ans[i] == -1) ans[i] = 1;  
           }  
           return ans;  
      }  
 };