From 70ea77c130864eac7255298519d1fd1c38374c9b Mon Sep 17 00:00:00 2001
From: prashansatanwar <prashansa18171@iiitd.ac.in>
Date: Sun, 3 Oct 2021 18:25:21 +0530
Subject: [PATCH 1/2] added 42 Trapping Rain Water C++

---
 .vscode/settings.json       |  5 +++++
 C++/trapping-rain-water.cpp | 35 +++++++++++++++++++++++++++++++++++
 README.md                   |  1 +
 3 files changed, 41 insertions(+)
 create mode 100644 .vscode/settings.json
 create mode 100644 C++/trapping-rain-water.cpp

diff --git a/.vscode/settings.json b/.vscode/settings.json
new file mode 100644
index 00000000..12d5f52b
--- /dev/null
+++ b/.vscode/settings.json
@@ -0,0 +1,5 @@
+{
+	"files.associations": {
+		"vector": "cpp"
+	}
+}
diff --git a/C++/trapping-rain-water.cpp b/C++/trapping-rain-water.cpp
new file mode 100644
index 00000000..47b1fed9
--- /dev/null
+++ b/C++/trapping-rain-water.cpp
@@ -0,0 +1,35 @@
+// https://leetcode.com/problems/trapping-rain-water/
+
+// Idea: 
+// We calculate the prefix and suffix max arrays 
+// The water trapped would be the min of the 2 arrays at a particular index minus the actual height 
+
+class Solution {
+public:
+    int trap(vector<int>& height) {
+        int n = height.size();
+        
+        if(n==0) return 0;
+        
+        vector<int> prefix(n);
+        vector<int> suffix(n);
+        
+        prefix[0] = height[0];
+        for(int i = 1; i<n; i++){
+            prefix[i] = max(prefix[i-1],height[i]);
+        }
+        
+        suffix[n-1] = height[n-1];
+        for(int i = n-2; i>=0; i--){
+            suffix[i] = max(suffix[i+1],height[i]);
+        }
+        
+        int ans = 0;
+        for(int i = 0; i<n; i++){
+            int x = min(prefix[i],suffix[i])-height[i];
+            if(x>0) ans+=x;         
+        }
+        
+        return ans;
+    }
+};
\ No newline at end of file
diff --git a/README.md b/README.md
index 36d17c18..4fa64e86 100644
--- a/README.md
+++ b/README.md
@@ -387,6 +387,7 @@ Check out ---> [Sample PR](https://github.com/codedecks-in/LeetCode-Solutions/pu
 | 174  | [Dungeon Game](https://leetcode.com/problems/dungeon-game/)                                                         | [C++](./C++/dungeon-game.pp)                              | _O(M\*N)_ | _O(M\*N)_ | Hard       | Dynamic Programming  |      |
 | 070  | [Climbing Stairs](https://leetcode.com/problems/climbing-stairs/)                                                   | [Java](./Java/climbing-stairs.java)                       | _O(N)_    | _O(1)_    | Easy       | DP                   |      |
 | 730  | [Count Different Palindromic Subsequences](https://leetcode.com/problems/count-different-palindromic-subsequences/) | [C++](./C++/Count-Different-Palindromic-Subsequences.cpp) | _O(N\*N)_ | _O(N\*N)_ | Hard       | DP                   |      |
+| 42  | [Trapping Rain Water](https://leetcode.com/problems/trapping-rain-water/) | [C++](./C++/trapping-rain-water.cpp) | _O(N)_ | _O(N)_ | Hard       | DP                   |      |
 
 <br/>
 <div align="right">

From 3f272ce9035d85817f8aba3969cc644b7d60b3b7 Mon Sep 17 00:00:00 2001
From: prashansatanwar <prashansa18171@iiitd.ac.in>
Date: Sun, 3 Oct 2021 18:30:02 +0530
Subject: [PATCH 2/2] added 42 Trapping Rain Water C++

---
 .vscode/settings.json | 5 -----
 1 file changed, 5 deletions(-)
 delete mode 100644 .vscode/settings.json

diff --git a/.vscode/settings.json b/.vscode/settings.json
deleted file mode 100644
index 12d5f52b..00000000
--- a/.vscode/settings.json
+++ /dev/null
@@ -1,5 +0,0 @@
-{
-	"files.associations": {
-		"vector": "cpp"
-	}
-}