From d6f2493f2c47031e0da57d8cf244ed7c48cd789e Mon Sep 17 00:00:00 2001
From: Neil Villamizar <neilvillamizar@gmail.com>
Date: Tue, 6 Oct 2020 19:00:55 -0400
Subject: [PATCH] Add solution to HISTOGRA problem from spoj

---
 histogra.cpp | 60 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 60 insertions(+)
 create mode 100644 histogra.cpp

diff --git a/histogra.cpp b/histogra.cpp
new file mode 100644
index 0000000..62ea698
--- /dev/null
+++ b/histogra.cpp
@@ -0,0 +1,60 @@
+    #include <iostream>
+    #include <vector>
+    #include <algorithm>
+    #include <cmath>
+    #include <string>
+    #include <queue>
+    #include <bits/stdc++.h>
+    #include <stack>
+     
+    using namespace std;
+     
+    #define FOR(i,n,m) for(int i=n; i<m; i++)
+    #define ROF(i,n,m) for(int i=n; i>m; i--)
+    #define pb push_back
+    #define ll long long
+    #define ri(a)  scanf("%d",&a)
+    #define rii(a,b)  scanf("%d %d",&a,&b)
+     
+     
+    /*--------------------------------------------------------------------------------------------------------------------------------------
+    --------------------------------------------------------------------------------------------------------------------------------------*/
+    ll n,ans,i;
+    ll a[200005];
+      
+    int main()
+    {
+        //ios_base::sync_with_stdio(false);
+        //cin.tie(NULL);
+     
+        cin>>n;
+     
+        while(n!=0){
+     
+            FOR(j,0,n) cin>>a[j];
+     
+           ans=0,i=0; stack<int> s;
+     
+            while(i<n){
+     
+                if(s.empty() || a[s.top()]<=a[i]) s.push(i++);
+                else{
+                    int minact=s.top(); s.pop();
+                    ll x= a[minact]*(s.empty()? i: i-1-s.top());
+                    ans=max(ans,x);
+                }
+     
+            }
+     
+            while(!s.empty()){
+                int minact=s.top(); s.pop();
+                ll x= a[minact]*(s.empty()? i: i-1-s.top());
+                ans=max(ans,x);
+            }
+     
+            cout<<ans<<endl;
+     
+            cin>>n;
+        }
+       
+    }