leetcode-1496-easy

Path Crossing

Given a string path, where path[i] = 'N', 'S', 'E' or 'W', each representing moving one unit north, south, east, or west, respectively. You start at the origin (0, 0) on a 2D plane and walk on the path specified by path.

Return true if the path crosses itself at any point, that is, if at any time you are on a location you have previously visited. Return false otherwise.

Example 1:


Input: path = "NES"
Output: false 
Explanation: Notice that the path doesn't cross any point more than once.
Example 2:


Input: path = "NESWW"
Output: true
Explanation: Notice that the path visits the origin twice.
Constraints:

1 <= path.length <= 104
path[i] is either 'N', 'S', 'E', or 'W'.

思路一：模拟操作，用 set 存储坐标点

    public boolean isPathCrossing(String path) {
        char[] chars = path.toCharArray();
        
        int x = 0;
        int y = 0;
        Set<String> set = new HashSet<>();
        set.add("0 0");
        for (char c : chars) {

            if (c == 'N') {
                y++;
            } else if (c == 'S') {
                y--;
            } else if (c == 'W') {
                x--;
            } else {
                x++;
            } 
            
            String key = x + " " + y;
            if (set.contains(key)) {
                return true;
            }

            set.add(key);
        }

        return false;
    }