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Java-based LeetCode algorithm problem solutions, regularly updated
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package g1401_1500.s1496_path_crossing;

// #Easy #String #Hash_Table #2022_03_23_Time_1_ms_(97.41%)_Space_42.9_MB_(31.41%)

import java.util.ArrayDeque;
import java.util.Deque;
import java.util.Objects;

/**
 * 1496 - Path Crossing\.
 *
 * Easy
 *
 * 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'`.
**/
public class Solution {
    public boolean isPathCrossing(String path) {
        Deque visited = new ArrayDeque<>();
        visited.add(new Coord(0, 0));
        for (char c : path.toCharArray()) {
            Coord last = visited.peek();
            if (c == 'N') {
                Coord nextStep = new Coord(last.x, last.y + 1);
                if (visited.contains(nextStep)) {
                    return true;
                }
                visited.add(nextStep);
            } else if (c == 'S') {
                Coord nextStep = new Coord(last.x, last.y - 1);
                if (visited.contains(nextStep)) {
                    return true;
                }
                visited.add(nextStep);
            } else if (c == 'E') {
                Coord nextStep = new Coord(last.x - 1, last.y);
                if (visited.contains(nextStep)) {
                    return true;
                }
                visited.add(nextStep);
            } else if (c == 'W') {
                Coord nextStep = new Coord(last.x + 1, last.y);
                if (visited.contains(nextStep)) {
                    return true;
                }
                visited.add(nextStep);
            }
        }
        return false;
    }

    private static class Coord {
        int x;
        int y;

        public Coord(int x, int y) {
            this.x = x;
            this.y = y;
        }

        @Override
        public boolean equals(Object o) {
            if (this == o) {
                return true;
            }
            if (o == null || getClass() != o.getClass()) {
                return false;
            }
            Coord coord = (Coord) o;
            return x == coord.x && y == coord.y;
        }

        @Override
        public int hashCode() {
            return Objects.hash(x, y);
        }
    }
}