LeetCode 第 159 场周赛

一、 缀点成线(LeetCode-5230)

1.1 题目描述

1.2 解题思路

比较简单的一题，利用公式 y = kx + b,确定好k和b就好，并且要考虑一种情况，函数 x = h。

1.3 解题代码

public boolean checkStraightLine(int[][] coordinates) {
        int k = Integer.MIN_VALUE;
        int x1 = coordinates[0][0];
        int y1 = coordinates[0][1];
        int x2 = coordinates[1][0];
        int y2 = coordinates[1][1];
        int dy = y2 - y1;
        int dx = x2 - x1;
        if (dx != 0) {
            k = dy / dx;
        }
        int b = y1 - k * x1;
        boolean onLine = true;
        for (int i = 2; i < coordinates.length; i++) {
            if (k == Integer.MIN_VALUE) {
                if (coordinates[i][0] != x1) {
                    onLine = false;
                    break;
                }
            } else if (coordinates[i][1] != (k * (coordinates[i][0]) + b)) {
                onLine = false;
                break;
            }
        }
        return onLine;
    }

二、 删除子文件夹(LeetCode-5231)

2.1 题目描述

2.2 解题思路

使用两层for循环会导致超时，需要使用字典树解决。

2.3 解题代码

class Solution {

    public Tree rootNode = null;

    public List<String> removeSubfolders(String[] folder) {

        rootNode = new Tree();
        rootNode.path = "/";
        rootNode.nextMap = new HashMap<>();

        List<String> res = new ArrayList<>();
        Arrays.sort(folder, (a, b) -> {
            return a.length() - b.length();
        });
        for (int i = 0; i < folder.length; i++) {
            if (!isCover(folder[i])) {
                res.add(folder[i]);
            }
        }
        return res;
    }

    public boolean isCover(String path) {

        boolean cover = false;
        String[] pathArray = path.split("/");
        int arrayLen = pathArray.length;

        Tree tmp = rootNode;
        for (int i = 1; i < arrayLen; i++) {
            Tree node = tmp.nextMap.get(pathArray[i]);
            if (node == null) {
                node = new Tree();
                node.path = pathArray[i];
                node.nextMap = new HashMap<>();
            } else {
                if (node.isRoot) {
                    cover = true;
                }
            }
            if (cover == false && i == arrayLen - 1) {
                node.isRoot = true;
            }
            tmp.nextMap.put(pathArray[i], node);
            tmp = node;
        }
        return cover;
    }

}

class Tree {
    public String path;
    //判断是否是根文件夹
    //例如 /a/b 可能是根文件夹，需要在b节点，记录isRoot = true;
    public boolean isRoot;
    public Map<String, Tree> nextMap;
}