LeetCode 657. Judge Route Circle

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

题意：在（0,0）处有一个机器人，给它一系列动作，判断机器人完成这一系列动作后能否返回原位置。
动作为：R右；L左；U上；D下。移动顺序是由这四个方向字符组成的字符串，输出true或false，表示机器人是否回到原位置。

思路：假定：向右走加1， 向左走减1；向上走加2，向下走减2。
将字符串转成字符数组，定义一个求和变量sum，逐个遍历每个字符，对每个字符根据其对应的数字进行加减，如果遍历完成后，sum为0，说明机器人回到了原位置；否则就没有回到原位置。代码如下：

public boolean judgeCircle(String moves) {
        char[] chars = moves.toCharArray();
        int sum = 0;
        for (int i = 0; i < chars.length; i++) {
            if (chars[i] == 'R')
                sum += 1;
            else if (chars[i] == 'L')
                sum -= 1;
            else if (chars[i] == 'U')
                sum += 2;
            else if (chars[i] == 'D')
                sum -= 2;
        }
        return sum == 0 ? true : false;
    }