Update areaHistogram.cpp

Lecture056 Stacks Questions/areaHistogram.cpp

@@ -1,62 +1,125 @@
+
+#include <vector>
+#include <stack>
+#include <climits>
+using namespace std;
+
 class Solution {
 private:
-    vector<int> nextSmallerElement(vector<int> arr, int n) {
+    // Function to find the next smaller element's index for each element
+    vector<int> nextSmallerElement(const vector<int>& arr, int n) {
         stack<int> s;
-        s.push(-1);
-        vector<int> ans(n);
+        vector<int> ans(n, n);  // Initialize with 'n' assuming no smaller element to the right
 
-        for(int i=n-1; i>=0 ; i--) {
-            int curr = arr[i];
-            while(s.top() != -1 && arr[s.top()] >= curr)
-            {
+        for (int i = n - 1; i >= 0; i--) {
+            while (!s.empty() && arr[s.top()] >= arr[i]) {
                 s.pop();
             }
-            //ans is stack ka top
-            ans[i] = s.top();
+            if (!s.empty()) {
+                ans[i] = s.top();
+            }
             s.push(i);
         }
         return ans;
     }
-
-    vector<int> prevSmallerElement(vector<int> arr, int n) {
+
+    // Function to find the previous smaller element's index for each element
+    vector<int> prevSmallerElement(const vector<int>& arr, int n) {
         stack<int> s;
-        s.push(-1);
-        vector<int> ans(n);
+        vector<int> ans(n, -1);  // Initialize with '-1' assuming no smaller element to the left
 
-        for(int i=0; i<n; i++) {
-            int curr = arr[i];
-            while(s.top() != -1 && arr[s.top()] >= curr)
-            {
+        for (int i = 0; i < n; i++) {
+            while (!s.empty() && arr[s.top()] >= arr[i]) {
                 s.pop();
             }
-            //ans is stack ka top
-            ans[i] = s.top();
+            if (!s.empty()) {
+                ans[i] = s.top();
+            }
             s.push(i);
         }
-        return ans; 
+        return ans;
     }
-    
+
 public:
     int largestRectangleArea(vector<int>& heights) {
-        int n= heights.size();
+        int n = heights.size();
+
+        // Get next and previous smaller elements' indices
+        vector<int> next = nextSmallerElement(heights, n);
+        vector<int> prev = prevSmallerElement(heights, n);
+
+        int maxArea = 0;
+
+        // Calculate area for each histogram bar
+        for (int i = 0; i < n; i++) {
+            int height = heights[i];
+            int width = next[i] - prev[i] - 1;  // Calculate width of the rectangle
+            int area = height * width;
+            maxArea = max(maxArea, area);  // Update max area
+        }
+
+        return maxArea;
+    }
+};
+// class Solution {
+// private:
+//     vector<int> nextSmallerElement(vector<int> arr, int n) {
+//         stack<int> s;
+//         s.push(-1);
+//         vector<int> ans(n);
+
+//         for(int i=n-1; i>=0 ; i--) {
+//             int curr = arr[i];
+//             while(s.top() != -1 && arr[s.top()] >= curr)
+//             {
+//                 s.pop();
+//             }
+//             //ans is stack ka top
+//             ans[i] = s.top();
+//             s.push(i);
+//         }
+//         return ans;
+//     }
+
+//     vector<int> prevSmallerElement(vector<int> arr, int n) {
+//         stack<int> s;
+//         s.push(-1);
+//         vector<int> ans(n);
+
+//         for(int i=0; i<n; i++) {
+//             int curr = arr[i];
+//             while(s.top() != -1 && arr[s.top()] >= curr)
+//             {
+//                 s.pop();
+//             }
+//             //ans is stack ka top
+//             ans[i] = s.top();
+//             s.push(i);
+//         }
+//         return ans; 
+//     }
+
+// public:
+//     int largestRectangleArea(vector<int>& heights) {
+//         int n= heights.size();
 
-        vector<int> next(n);
-        next = nextSmallerElement(heights, n);
+//         vector<int> next(n);
+//         next = nextSmallerElement(heights, n);
 
-        vector<int> prev(n);
-        prev = prevSmallerElement(heights, n);
+//         vector<int> prev(n);
+//         prev = prevSmallerElement(heights, n);
 
-        int area = INT_MIN;
-        for(int i=0; i<n; i++) {
-            int l = heights[i];
+//         int area = INT_MIN;
+//         for(int i=0; i<n; i++) {
+//             int l = heights[i];
 
-            if(next[i] == -1) {
-                next[i] = n;
-            }
-             int b = next[i] - prev[i] - 1;
-            int newArea = l*b;
-            area = max(area, newArea);
-        }
-        return area;
-    }
-};
+//             if(next[i] == -1) {
+//                 next[i] = n;
+//             }
+//              int b = next[i] - prev[i] - 1;
+//             int newArea = l*b;
+//             area = max(area, newArea);
+//         }
+//         return area;
+//     }
+// };