84.cpp

largest area of histogram

Author: udaysrinu

Diff for: 84.cpp

@@ -0,0 +1,124 @@
+class Solution {
+public:
+    int largestRectangleArea(vector<int>& A) {
+         int n=A.size();
+    stack<int>s;
+    vector<int>nsr;
+    for(int i=n-1;i>=0;i--)
+    {
+        if(s.empty())
+        {
+            nsr.push_back(n);
+        }
+        else if(A[s.top()]<A[i])
+        {
+            nsr.push_back(s.top());
+        }
+        else if(A[s.top()]>=A[i])
+        {
+            while(!s.empty()&&A[s.top()]>=A[i])
+            {
+                s.pop();
+            }
+            if(s.empty())
+            {
+                nsr.push_back(n);
+            }
+            else
+            nsr.push_back(s.top());
+        }
+        s.push(i);
+    }
+    reverse(nsr.begin(),nsr.end());
+    stack<int>ss;
+    vector<int>nsl;
+    for(int i=0;i<n;i++)
+    {
+        if(ss.empty())
+        {
+            nsl.push_back(-1);            
+        }
+        else if(A[ss.top()]<A[i])
+        {
+            nsl.push_back(ss.top());
+        }
+        else if(A[ss.top()]>=A[i])
+        {
+            while(!ss.empty()&&A[ss.top()]>=A[i])
+            ss.pop();
+            if(ss.empty())
+            {
+                nsl.push_back(-1);
+            }
+            else
+            nsl.push_back(ss.top());
+        }
+        ss.push(i);
+    }
+    int ans=0;
+    for(int i=0;i<n;i++)
+    {
+        ans=max(ans,(nsr[i]-nsl[i]-1)*A[i]);
+    }
+    return ans;  n=A.size();
+    stack<int>s;
+    vector<int>nsr;
+    for(int i=n-1;i>=0;i--)
+    {
+        if(s.empty())
+        {
+            nsr.push_back(n);
+        }
+        else if(A[s.top()]<A[i])
+        {
+            nsr.push_back(s.top());
+        }
+        else if(A[s.top()]>=A[i])
+        {
+            while(!s.empty()&&A[s.top()]>=A[i])
+            {
+                s.pop();
+            }
+            if(s.empty())
+            {
+                nsr.push_back(n);
+            }
+            else
+            nsr.push_back(s.top());
+        }
+        s.push(i);
+    }
+    reverse(nsr.begin(),nsr.end());
+    stack<int>ss;
+    vector<int>nsl;
+    for(int i=0;i<n;i++)
+    {
+        if(ss.empty())
+        {
+            nsl.push_back(-1);            
+        }
+        else if(A[ss.top()]<A[i])
+        {
+            nsl.push_back(ss.top());
+        }
+        else if(A[ss.top()]>=A[i])
+        {
+            while(!ss.empty()&&A[ss.top()]>=A[i])
+            ss.pop();
+            if(ss.empty())
+            {
+                nsl.push_back(-1);
+            }
+            else
+            nsl.push_back(ss.top());
+        }
+        ss.push(i);
+    }
+    int ans=0;
+    for(int i=0;i<n;i++)
+    {
+        ans=max(ans,(nsr[i]-nsl[i]-1)*A[i]);
+    }
+    return ans;
+    }
+};