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
题目含义：初始位于坐标(0, 0)，UDLR分别表示向上下左右移动，求移动结束后是否位于原点。

    public boolean judgeCircle(String moves) {
        int x = 0;
        int y = 0;
        for (char ch : moves.toCharArray()) {
            if (ch == 'U') x--;
            else if (ch == 'D') x++;
            else if (ch == 'R') y++;
            else if (ch == 'L') y--;
        }
        return x == 0 && y == 0;    
    }