Leetcode:657. Judge Route Circle (week 7)

Description:

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

解題思路分析

本題判斷移動後是否回到原點，解題思路很簡單：首先聲明兩個int型變量x,y作爲座標，遍歷字符串若爲R則x++,若爲L則x–,若爲U則y++,若爲D則y–；遍歷結束後比較x,y是否爲0 =，均爲0則返回true。
時間複雜度爲O(n),n爲字符串長度。

代碼

class Solution {
public:
    bool judgeCircle(string moves) {
        int x = 0, y = 0;
        for (std::string::iterator it=moves.begin(); it!=moves.end(); ++it) {
            if (*it == 'R') {
                x++;
            } else if (*it == 'L') {
                x--;
            } else if (*it == 'U') {
                y++;
            } else if (*it == 'D') {
                y--;
            }
        }
        if (x == 0 && y == 0) return true;
        return false;
    }
};