create 2017-grid-game.cpp

Author: Maunish-dave

Diff for: cpp/2017-grid-game.cpp

@@ -0,0 +1,33 @@
+/* 
+Approch:
+    2nd robot can collect either all the bottom points
+    before the break point (when 1st robot goes to bottom)
+    or collect all the top points after that break point.
+Time Complexity: O(N)
+Space Complexity: O(1)
+*/
+
+class Solution {
+public:
+    long long gridGame(vector<vector<int>>& grid) {
+  
+        // prefix sum
+        long long top = grid[0][0],bottom = 0, answer = LONG_MAX;
+        for(int i =1;i<grid[0].size();i++){
+            top += grid[0][i];
+        }
+
+        for(int i =0;i<grid[0].size();i++){
+            // All the top points 2nd robot can collect
+            top -= grid[0][i];
+
+            // min because first robot wants to  minimize 
+            answer = min(answer,max(top,bottom));
+
+            // All the bootom points the robot could collect
+            bottom += grid[1][i];
+        }
+
+        return answer;
+    }
+};