Added area under histogram

Author: avidLearnerInProgress

amazon/area_under_histogram.cpp

@@ -0,0 +1,54 @@
+#include<bits/stdc++.h>
+using namespace std;
+
+long long maxArea(long long a[],long long n){
+    stack<long long> s;
+    long long max_area=0;
+    long long area_with_top;
+    long long top;
+    
+    long long i=0;
+    while(i<n){
+        if(s.empty() || a[s.top()]<=a[i]) //check if curr is > than curr_top
+            s.push(i++); //i++ because starting from 0 
+            
+        else{
+            top=s.top(); 
+            s.pop();
+            area_with_top=a[top]*(s.empty() ? i: i-s.top() -1);
+            
+            if(max_area<area_with_top)
+                max_area=area_with_top;
+                
+        }
+    }
+    
+    
+    while(!s.empty()){
+            top=s.top();
+            s.pop();
+            area_with_top=a[top]*(s.empty() ? i: i-s.top() -1);
+            
+            if(max_area<area_with_top)
+                max_area=area_with_top;
+                
+    }
+    return max_area;
+}
+
+int main()
+ {
+	//code
+        long long T;
+        cin>>T;
+        while(T--)
+        { 
+            long long n;cin>>n;
+            long long arr[n];
+            for(long long i=0;i<n;i++)cin>>arr[i];
+            
+            long long res=maxArea(arr,n);
+            cout<<res<<endl;
+        }
+	return 0;
+}