Problem
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 <= 104path[i]is either'N','S','E', or'W'.
Solution
/**
* @param {string} path
* @return {boolean}
*/
var isPathCrossing = function(path) {
var num = 0;
var map = {
N: 1,
S: -1,
E: 10000,
W: -10000,
};
var visited = { '0': true };
for (var i = 0; i < path.length; i++) {
num += map[path[i]];
if (visited[num]) return true;
visited[num] = true;
}
return false;
};
Explain:
nope.
Complexity:
- Time complexity : O(n).
- Space complexity : O(n).