Time: 208 ms (53.09%), Space: 81.4 MB (55.79%) - LeetHub

Author: knockcat

0084-largest-rectangle-in-histogram/0084-largest-rectangle-in-histogram.cpp

@@ -0,0 +1,82 @@
+class Solution {
+public:
+    int largestRectangleArea(vector<int>& heights) {
+        
+        int n = heights.size();
+        
+        vector<int> leftSmall(n), rightSmall(n);
+        
+        stack<int> st;
+        
+        for(int i = 0; i < n; ++i)
+        {
+            if(st.empty())
+            {
+                st.push(i);
+                leftSmall[i] = 0;
+            }
+            else if(heights[st.top()] >= heights[i])
+            {
+                while(!st.empty() and heights[st.top()] >= heights[i])
+                    st.pop();
+                
+                if(st.empty())
+                    leftSmall[i] = 0;
+                else
+                    leftSmall[i] = st.top() +1;
+                st.push(i);
+            }
+            else
+            {
+                leftSmall[i] = st.top() + 1;
+                st.push(i);
+            }
+        }
+        
+        // for(auto itr : leftSmall)
+        //     cout<<itr<<" ";
+        // cout<<endl;
+        
+        while(!st.empty())
+            st.pop();
+        
+        for(int i = n-1; i >= 0; --i)
+        {
+            if(st.empty())
+            {
+                st.push(i);
+                rightSmall[i] = n-1;
+            }
+            else if(heights[st.top()] >= heights[i])
+            {
+                while(!st.empty() and heights[st.top()] >= heights[i])
+                    st.pop();
+                if(st.empty())
+                    rightSmall[i] = n-1;
+                else
+                    rightSmall[i] = st.top() - 1;
+                st.push(i);
+            }
+            else{
+                rightSmall[i] = st.top() - 1;
+                st.push(i);
+            }
+        }
+        
+        
+        // for(auto itr : rightSmall)
+        //     cout<<itr<<" ";
+        // cout<<endl;
+        
+        int ans = 0;
+        
+        for(int i =0 ; i<n; ++i)
+        {
+            ans = max(ans, heights[i] * (rightSmall[i] - leftSmall[i] + 1));
+            // cout<<ans<<endl;
+        }
+        
+        return ans;
+        
+    }
+};