657. Judge Route Circle.cpp

 /*
 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
*/
class Solution {
public:
    bool judgeCircle(string moves) {
        if(moves=="")
            return true;
        int a[90]={0};
        int i = 0;
        
        while(moves[i])
        {
            ++a[moves[i++]];
        }
        
        if(a[82]==a[76] && a[85]==a[68])
            return true;
        else
            return false;        
    }
};