1496. Path Crossing

QUESTION:

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'.

EXPLANATION:

比较简单, 就不多做说明了.

SOLUTION:

class Solution {
    fun isPathCrossing(path: String): Boolean {
        var visited = ArrayList<Pair<Int,Int>>()
        var start:Pair<Int,Int> = Pair(0,0)
        visited.add(start)
        for (p in path) {
            when (p) {
                'N' -> {
                    start = start.copy(second = start.second + 1)
                }
                'S' -> {
                    start = start.copy(second = start.second - 1)
                }
                'E' -> {
                    start = start.copy(first = start.first + 1)
                }
                'W' -> {
                    start = start.copy(first = start.first - 1)
                }
            }
            var tmp = Pair(start.first, start.second)
            if (visited.contains(tmp)) return true
            else visited.add(tmp)
        }
        return false
    }
}
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