Trapping rain water problem using c++(Optimised)

Arrays/trappingrainwater.cpp

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+// Given an array of numbers which are heights to the container, we need to find upto what maximum value water can be filled in this vessel
+// of different heights.
+// Time complexity - O(n)
+//Space complexity - O(1)
+#include<bits/stdc++.h>
+using namespace std;
+
+int main(){
+    int arr[]={1,8,6,2,5,4,8,3,7}; //array of diff heights
+    int l=0,n=sizeof(arr)/sizeof(int),r=n-1;
+    int max_area=0,h,a,b;
+    //2 pointers algorithm
+
+    while(l<r){ 
+        h=min(arr[l],arr[r]); //choosing the minimum of both heights -left and right side
+        b=r-l; //base = right height index - left 
+        a=h*b;
+        max_area=max(a,max_area); //idea to maximize the area to trap more water
+        if(arr[l]<=arr[r]){
+            l++; //if right ride height is greater move left pointer to choose max of heights
+        }
+        else{
+            r--; //else move right pointer to choose next max height
+        }
+    }
+    cout<<"Maximum water that can be trapped is : "<<max_area;
+    return 0;
+
+}