LeetCode 657. Judge Route Circle

problem:

 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

 

first:

import java.util.Stack;

class Solution {
    public boolean judgeCircle(String moves) {
        Stack<Character> stack = new Stack<Character>();
        for(int i=0;i<moves.length();i++){
            if(stack.size()==0){
                stack.push(moves.charAt(i));
            } else if(stack.peek()=='U'&&moves.charAt(i)=='D'||
                      stack.peek()=='D'&&moves.charAt(i)=='U'||
                      stack.peek()=='L'&&moves.charAt(i)=='R'||
                      stack.peek()=='R'&&moves.charAt(i)=='L'){
                stack.pop();
            } else {
                stack.push(moves.charAt(i));
            }
        }
        
        return stack.empty() ? true : false;
    }
}

 result:

Submission Result: Wrong Answer 

 

Input: "RLUURDDDLU"

Output: false

Expected: true

 

2:

import java.util.Stack;

class Solution {
    public boolean judgeCircle(String moves) {
        int rCounts=0, lCounts=0,dCounts=0,uCounts=0;
        for(int i=0;i<moves.length();i++){
            if(moves.charAt(i)=='U'){
                uCounts++;
            }
            if(moves.charAt(i)=='D'){
                dCounts++;
            }
            if(moves.charAt(i)=='R'){
                rCounts++;
            }
            if(moves.charAt(i)=='L'){
                lCounts++;
            }
        }
        
        return uCounts==dCounts&&rCounts==lCounts ? true : false;
    }
}

 

result:

 

参考答案：

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

 

result：

retry:

class Solution {
    public boolean judgeCircle(String moves) {
        int rCounts=0, lCounts=0,dCounts=0,uCounts=0;
        char[] charArray = moves.toCharArray();
        for(int i=0;i<charArray.length;i++){
            if(charArray[i]=='U'){
                uCounts++;
            }
            if(charArray[i]=='D'){
                dCounts++;
            }
            if(charArray[i]=='R'){
                rCounts++;
            }
            if(charArray[i]=='L'){
                lCounts++;
            }
        }
        
        return uCounts==dCounts&&rCounts==lCounts ? true : false;
    }
}

 

result:

 

conclusion:

 

可见把String转换成char数组后效率更高。