Added 'Robot Bounded In Circle'

Author: anthonyzhub

Robot Bounded In Circle.java

@@ -0,0 +1,60 @@
+// https://leetcode.com/problems/robot-bounded-in-circle/
+
+/*
+ * Breakdown of the for-loop from Leetcode:
+ * 
+ * 
+
+    Now everything is ready to iterate over the instructions.
+
+    If the current instruction is R, i.e. to turn on the right, the next direction is idx = (idx + 1) % 4.
+    Modulo here is needed to deal with the situation - facing west, idx = 3, turn to the right to face north, idx = 0.
+
+    If the current instruction is L, i.e. to turn on the left, the next direction could written in a
+    symmetric way idx = (idx - 1) % 4. That means we have to deal with negative indices. A more simple
+    way is to notice that 1 turn to the left = 3 turns to the right: idx = (idx + 3) % 4.
+
+    If the current instruction is to move, we simply update the coordinates: x += directions[idx][0],
+    y += directions[idx][1].
+
+ *
+ * 
+ */
+
+class Solution {
+    public boolean isRobotBounded(String instructions) {
+
+        /*
+         * Time Complexity: O(n) where n = length of instructions
+         * 
+         * Space Complexity: O(n) where n = length of char array, which is based on instructions' length
+         */
+        
+        // Create a list of directions
+        int dir[][] = {{0,1}, {-1, 0}, {0, -1}, {1,0}};
+        int i = 0;
+
+        // Define initial position
+        int x = 0;
+        int y = 0;
+
+        // Iterate instructions
+        for (char c: instructions.toCharArray()) {
+            
+            if(c == 'L'){
+                i = (i + 1) % 4;
+            }
+            else if (c == 'R') {
+                i = (i + 3) % 4;
+            }
+            else {
+                x = x + dir[i][0];
+                y = y + dir[i][1];
+            }
+
+        }
+
+        // If either robot changed position or direction, return true. If not, return false
+        return x == 0 && y == 0 || i != 0;
+    }
+}