657. Robot Return to Origin

Problem 657

https://leetcode.com/problems/robot-return-to-origin/

There is a robot starting at position (0, 0), the origin, on a 2D plane. Given a sequence of its moves, judge if this robot ends up at (0, 0) after it completes its moves.

The move sequence is represented by a string, and the character moves[i] represents its ith move. Valid moves are R (right), L (left), U (up), and D (down). If the robot returns to the origin after it finishes all of its moves, return true. Otherwise, return false.

Example 1:

Input: "UD"
Output: true 
Explanation: The robot moves up once, and then down once. All moves have the same magnitude, so it ended up at the origin where it started. Therefore, we return true.

Solution

Complex Number

class Solution_ComplexNumber(object):
    def judgeCircle(self, moves):
        """
        :type moves: str
        :rtype: bool
        """
        walk = {'U':1,'D':-1,'L':1j,'R':-1j}
        
        return sum( walk[move] for move in moves ) == 0

dictionary

class Solution(object):
    def judgeCircle(self, moves):

        walk = {'U':1,'L':1,'D':-1,'R':-1}
        stepLR, stepUD = 0, 0
        for move in moves:
            if move in ['L','R']:
                stepLR += walk[move]
            else:
                stepUD += walk[move]
        
        return (stepUD==0) & (stepLR==0)

count

class Solution_count(object):
    def judgeCircle(self, moves):
        
        return moves.count('L') == moves.count('R') and moves.count('U') == moves.count('D')

Collection

class Solution_collection(object):
    def judgeCircle(self, moves):

        walk = collections.Counter(moves)
        return walk['L'] == walk['R'] and walk['U'] == walk['D']