问题描述
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

Input: "UD"
Output: true
Input: "LLRUDRR"
Output: false

思路：设置两个计数器，根据走的路线来判断是++还是–，最后都为0则回到原点

 * @param {string} moves
 * @return {boolean}
 */
var judgeCircle = function(moves) {
    var x = 0;
    var y = 0;
    for(var i = 0; i < moves.length; i++){
        if(moves.charAt(i) === 'R'){
            x++;
        }
        if(moves.charAt(i) === 'L'){
            x--;
        }
        if(moves.charAt(i) === 'U'){
            y++;
        }
        if(moves.charAt(i) === 'D'){
            y--;
        }
    }
    if( x===0 && y===0){
        return true;
    }
    else{return false;}
};