42. Trapping Rain Water #Hard

Author: SjxSubham

42. Trapping Rain Water

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+//Here is the two pointer approach
+//by taking auxaliary space of O(n)
+
+//Here I'm giving Both C++ & java Solution
+
+// C++  Solution                                                             //and for java solution scroll down 
+
+class Solution {
+public:
+    int trap(vector<int>&height) {
+        //Space COmplexity O(n)
+        //Time Complexity O(n)
+        int n = height.size();
+
+        vector<int>left(n);
+        left[0] = height[0];
+
+        for(int i=1;i<n;i++){
+            left[i] = max(left[i-1],height[i]);
+        }
+
+        vector<int>right(n);
+        right[n-1] = height[n-1];
+
+        for(int i=n-2;i>=0;i--){
+            right[i] = max(right[i+1],height[i]);
+        }
+        
+        int ans =0;
+        for(int i=0;i<n;i++){
+            ans += (min(right[i],left[i])-height[i]);
+        }
+        return ans;
+    
+    }
+};
+
+// Java Solution
+
+class Solution {
+    public int trap(int[] height) {
+        //SPace Complexitiy O(n)
+        int n = height.length;
+        int left[] = new int[n];
+        int right[] = new int[n];
+        left[0] = height[0];
+        for(int i=1;i<n;i++){
+            left[i] = Math.max(left[i-1],height[i]);
+        }
+        right[n-1] = height[n-1];
+        for(int i=n-2;i>=0;i--){
+            right[i] = Math.max(right[i+1],height[i]);
+        }
+        int ans=0;
+        for(int i=0;i<n;i++){
+            //formula
+            ans += (Math.min(left[i],right[i])-height[i]);
+        }
+        return ans;
+    }
+};
+
+