【LeetCode】657. Judge Route Circle 解题报告

【LeetCode】657. Judge Route Circle

标签（空格分隔）： LeetCode

题目地址：https://leetcode.com/problems/judge-route-circle/description/

题目描述：

Initially, there is a Robot at position (0, 0). Given a sequence of its moves, judge if this robot makes a circle, which means it moves back to the original place.

The move sequence is represented by a string. And each move is represent by a character. The valid robot moves are R (Right), L (Left), U (Up) and D (down). The output should be true or false representing whether the robot makes a circle.

Example 1:

Input: “UD”

Output: true

Example 2:

Input: “LL”

Output: false

Ways

python里面表达坐标比较简单，直接用列表就可以。

这个题就是判断移动了几次之后是否在原来的位置，只要每步都去修改一次即可。

方法一，O(n)：

class Solution:
def judgeCircle(self, moves):
"""
:type moves: str
:rtype: bool
"""
position = [0, 0]
for move in moves:
if move == 'R':
position[0] += 1
if move == 'L':
position[0] -= 1
if move == 'U':
position[1] += 1
if move == 'D':
position[1] -= 1
return position == [0, 0]

方法二，数左右移动的次数和上下移动的次数是否相等：

class Solution:
def judgeCircle(self, moves):
"""
:type moves: str
:rtype: bool
"""
return moves.count('L') == moves.count('R') and moves.count('U') == moves.count('D')

方法三，看了Discuss才知道，python原来也可以用复数！

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

Date

2018 年 1 月 13 日