leetcode

commit 2506f2bce7d5a1878bb54e814b478282fa0b9cc2
parent a938639a498879a8078db75a3e1ad060e574a021
Author: Jack Sangdahl <jack@pngu.org>
Date:   Sat,  4 Apr 2026 20:07:57 -0600

657. robot return to origin

Diffstat:
A
robot_return_origin.c
 | 
36
++++++++++++++++++++++++++++++++++++
A
robot_return_origin.py
 | 
23
+++++++++++++++++++++++

2 files changed, 59 insertions(+), 0 deletions(-)
diff --git a/robot_return_origin.c b/robot_return_origin.c
@@ -0,0 +1,36 @@
+// 657. Robot Return to Origin
+#include "leetcode.h"
+
+/*
+ * there is a robot starting at the position '(0, 0)', the origin, on a 2d
+ * plane. given a sequence of its move, judge if this robot ends up at '(0, 0)'
+ * after it completes its moves. you are given a string 'moves' that represents
+ * the move sequence of the robot where 'moves[i]' represents its i'th move.
+ * valid moves are R, L, U, D. return trueif the robot returns to the origin
+ * after it finishes all its moves, or false otherwise.
+ */
+
+bool judgeCircle(char *moves) {
+  uint64_t counts = 0;
+  for (int i = 0; moves[i] != '\0'; i++) {
+    uint64_t b = moves[i];
+    uint64_t m1 = (b * 0x0001000100010001ULL) | 0x0100010001000100ULL;
+    uint64_t m2 = m1 - 0x00550044004C0052ULL;
+    uint64_t m3 = m2 | (m2 >> 4);
+    uint64_t m4 = m3 | (m3 >> 2);
+    uint64_t m5 = m4 | (m4 >> 1);
+    uint64_t m6 = m5 | ((~m2 & 0x0100010001000100ULL) >> 8);
+    counts += (0x0001000100010001ULL & ~m6);
+  }
+  uint8_t *cs = (uint8_t *)&counts;
+  return cs[0] == cs[2] && cs[1] == cs[3] && cs[4] == cs[6] && cs[5] == cs[7];
+}
+int main() {
+  char *m1 = "UD", *m2 = "LL";
+  bool r1 = judgeCircle(m1);
+  bool r2 = judgeCircle(m2);
+  printf("%d\n", r1);
+  assert(r1 == true);
+  printf("%d\n", r2);
+  assert(r2 == false);
+}
diff --git a/robot_return_origin.py b/robot_return_origin.py
@@ -0,0 +1,23 @@
+# 657. Robot Return to Origin
+
+"""
+there is a robot starting at the position '(0, 0)', the origin, on a 2d
+plane. given a sequence of its move, judge if this robot ends up at '(0, 0)'
+after it completes its moves. you are given a string 'moves' that represents
+the move sequence of the robot where 'moves[i]' represents its i'th move.
+valid moves are R, L, U, D. return trueif the robot returns to the origin
+after it finishes all its moves, or false otherwise.
+"""
+
+
+class Solution:
+    def judgeCircle(self, moves: str) -> bool:
+        return moves.count("L") == moves.count("R") and moves.count("U") == moves.count(
+            "D"
+        )
+
+
+if __name__ == "__main__":
+    obj = Solution()
+    print(obj.judgeCircle(moves="UD"))
+    print(obj.judgeCircle(moves="LL"))