【Leetcode】1496. Path Crossing

题目地址：

https://leetcode.com/problems/path-crossing/

给定一个长$n$字符串$s$，代表平面直角坐标系的一条路径，路径从$(0,0)$出发，字符串只含'N', 'E', 'S', 'W'分别代表北东南西四个方向。问路径是否自交。

直角用哈希表记录下路径即可。代码如下：

import java.util.HashSet;
import java.util.Map;
import java.util.Objects;
import java.util.Set;

public class Solution {
    
    
    
    class Pair {
    
    
        int x, y;
        
        public Pair(int x, int y) {
    
    
            this.x = x;
            this.y = y;
        }
        
        @Override
        public boolean equals(Object o) {
    
    
            Pair pair = (Pair) o;
            return x == pair.x && y == pair.y;
        }
        
        @Override
        public int hashCode() {
    
    
            return Objects.hash(x, y);
        }
    }
    
    public boolean isPathCrossing(String path) {
    
    
        Set<Pair> set = new HashSet<>();
        set.add(new Pair(0, 0));
        
        int[] d = {
    
    1, 0, -1, 0, 1};
        Map<Character, Integer> map = Map.of('N', 3, 'S', 1, 'E', 0, 'W', 2);
        
        int x = 0, y = 0;
        for (int i = 0; i < path.length(); i++) {
    
    
            int idx = map.get(path.charAt(i));
            x += d[idx];
            y += d[idx + 1];
            Pair next = new Pair(x, y);
            if (set.contains(next)) {
    
    
                return true;
            }
            
            set.add(next);
        }
        
        return false;
    }
}

时空复杂度$O(n)$。