added trapping-rain-water.java code

Author: pranav-3005

Coding/Java/trapping-rain-water.java

@@ -0,0 +1,48 @@
+//Question : https://leetcode.com/problems/trapping-rain-water/description/
+
+class Solution {
+    public int trap(int[] h) {
+        int n=h.length;
+
+        //left and ryt boundary
+        int lb=h[0], rb=h[n-1];
+
+        //traversing range ,start and end within boundary
+        int l=1, r= n-2;
+
+        int tw=0; //total_water
+        
+        //traverse
+        while(l<=r)
+        {
+            if(lb<=rb)
+            {
+                int hw=lb; //theight of water (smallest of(left and ryt boundary))
+                
+                //whether water can be stored at top of building(h[l])
+                if(h[l]<hw)
+                {
+                    int ac= hw - h[l]; //actual height(i.e.. water on top of the building)
+                    tw+= ac; //add to total water
+                }
+                lb= Math.max(lb,h[l]);
+                l++;
+            }
+            else
+            {
+               int hw=rb; //tot height of water
+                
+                //whether water can be stored at top of building
+                if(h[r]<hw)
+                {
+                    int ac= hw - h[r]; //actual height(i.e.. water on top)
+                    tw+= ac;  //add to total water
+                }
+                rb= Math.max(rb,h[r]);
+                r--;
+            }
+        }
+        return tw;
+
+    }
+}