feat: solve No.1496

Author: BaffinLee

1401-1500/1496. Path Crossing.md

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+# 1496. Path Crossing
+
+- Difficulty: Easy.
+- Related Topics: Hash Table, String.
+- Similar Questions: .
+
+## 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:
+
+![](https://assets.leetcode.com/uploads/2020/06/10/screen-shot-2020-06-10-at-123929-pm.png)
+
+```
+Input: path = "NES"
+Output: false 
+Explanation: Notice that the path doesn't cross any point more than once.
+```
+
+Example 2:
+
+![](https://assets.leetcode.com/uploads/2020/06/10/screen-shot-2020-06-10-at-123843-pm.png)
+
+```
+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'`.
+
+
+
+## Solution
+
+```javascript
+/**
+ * @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).