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1548. 图中最相似的路径 🔒

题目描述

我们有 n 座城市和 m 条双向道路 roads ，其中 roads[i] = [ai, bi] 连接城市 ai 和城市 bi。每个城市的名称由字符串数组 names 中给出的三个大写英文字母组成。从任意城市 x 出发，你可以到达任意城市 y ，其中 y != x （即：城市和道路形成一张无向连通图）。

给定一个字符串数组 targetPath，你需要找出图中与 targetPath 的 长度相同 且 编辑距离最小 的路径。

你需要返回 编辑距离最小的路径中节点的顺序 。该路径应当与 targetPath 的长度相等，且路径需有效（即： ans[i] 和 ans[i + 1] 间应存在直接连通的道路）。如果有多个答案，返回任意一个。

编辑距离 的定义如下：

 

示例 1：

输入：n = 5, roads = [[0,2],[0,3],[1,2],[1,3],[1,4],[2,4]], names = ["ATL","PEK","LAX","DXB","HND"], targetPath = ["ATL","DXB","HND","LAX"]
输出：[0,2,4,2]
解释：[0,2,4,2], [0,3,0,2] 和 [0,3,1,2] 都是正确答案。
[0,2,4,2] 等价于 ["ATL","LAX","HND","LAX"] ，与 targetPath 的编辑距离 = 1。
[0,3,0,2] 等价于 ["ATL","DXB","ATL","LAX"] ，与 targetPath 的编辑距离 = 1。
[0,3,1,2] 等价于 ["ATL","DXB","PEK","LAX"] ，与 targetPath 的编辑距离 = 1。

示例 2：

输入：n = 4, roads = [[1,0],[2,0],[3,0],[2,1],[3,1],[3,2]], names = ["ATL","PEK","LAX","DXB"], targetPath = ["ABC","DEF","GHI","JKL","MNO","PQR","STU","VWX"]
输出：[0,1,0,1,0,1,0,1]
解释：任意路径与 targetPath 的编辑距离都等于 8。

示例 3：

输入：n = 6, roads = [[0,1],[1,2],[2,3],[3,4],[4,5]], names = ["ATL","PEK","LAX","ATL","DXB","HND"], targetPath = ["ATL","DXB","HND","DXB","ATL","LAX","PEK"]
输出：[3,4,5,4,3,2,1]
解释：[3,4,5,4,3,2,1] 是唯一与 targetPath 的编辑距离 = 0 的路径。
该路径等价于 ["ATL","DXB","HND","DXB","ATL","LAX","PEK"]

 

提示：

  • 2 <= n <= 100
  • m == roads.length
  • n - 1 <= m <= (n * (n - 1) / 2)
  • 0 <= ai, bi <= n - 1
  • ai != bi 
  • 给定的图保证是连通的，任意两个节点至多有一个直接连通的道路。
  • names.length == n
  • names[i].length == 3
  • names[i] 包含大写英文字母。
  • 可能有两个名称相同的城市。
  • 1 <= targetPath.length <= 100
  • targetPath[i].length == 3
  • targetPath[i] 由大写英文字母组成。

 

进阶：如果路径中每个节点只可访问一次，你该如何修改你的答案？

解法

方法一：动态规划

我们先根据给定的道路构建一个邻接表 $g$，其中 $g[i]$ 表示与城市 $i$ 直接相连的城市列表。

然后我们定义 $f[i][j]$ 表示 $targetPath$ 的第 $i$ 个城市与 $names$ 的第 $j$ 个城市匹配时，前 $i$ 个城市的最小编辑距离。

那么我们可以得到状态转移方程：

$$ f[i][j] = \min_{k \in g[j]} f[i - 1][k] + (targetPath[i] \neq names[j]) $$

在状态转移的过程中，我们记录下每个状态的前驱城市，最后根据前驱城市数组 $pre$ 从后往前还原出最优路径。

时间复杂度 $O(m \times n^2)$，空间复杂度 $O(m \times n)$。其中 $m$ 和 $n$ 分别是 $targetPath$ 和 $names$ 的长度。

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class Solution:
    def mostSimilar(
        self, n: int, roads: List[List[int]], names: List[str], targetPath: List[str]
    ) -> List[int]:
        g = [[] for _ in range(n)]
        for a, b in roads:
            g[a].append(b)
            g[b].append(a)
        m = len(targetPath)
        f = [[inf] * n for _ in range(m)]
        pre = [[-1] * n for _ in range(m)]
        for j, s in enumerate(names):
            f[0][j] = targetPath[0] != s
        for i in range(1, m):
            for j in range(n):
                for k in g[j]:
                    if (t := f[i - 1][k] + (targetPath[i] != names[j])) < f[i][j]:
                        f[i][j] = t
                        pre[i][j] = k
        k = 0
        mi = inf
        for j in range(n):
            if f[-1][j] < mi:
                mi = f[-1][j]
                k = j
        ans = [0] * m
        for i in range(m - 1, -1, -1):
            ans[i] = k
            k = pre[i][k]
        return ans

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class Solution {
    public List<Integer> mostSimilar(int n, int[][] roads, String[] names, String[] targetPath) {
        List<Integer>[] g = new List[n];
        Arrays.setAll(g, i -> new ArrayList<>());
        for (int[] r : roads) {
            int a = r[0], b = r[1];
            g[a].add(b);
            g[b].add(a);
        }
        int m = targetPath.length;
        final int inf = 1 << 30;
        int[][] f = new int[m][n];
        int[][] pre = new int[m][n];
        for (int i = 0; i < m; i++) {
            Arrays.fill(f[i], inf);
            Arrays.fill(pre[i], -1);
        }
        for (int j = 0; j < n; ++j) {
            f[0][j] = targetPath[0].equals(names[j]) ? 0 : 1;
        }
        for (int i = 1; i < m; ++i) {
            for (int j = 0; j < n; ++j) {
                for (int k : g[j]) {
                    int t = f[i - 1][k] + (targetPath[i].equals(names[j]) ? 0 : 1);
                    if (t < f[i][j]) {
                        f[i][j] = t;
                        pre[i][j] = k;
                    }
                }
            }
        }
        int mi = inf, k = 0;
        for (int j = 0; j < n; ++j) {
            if (f[m - 1][j] < mi) {
                mi = f[m - 1][j];
                k = j;
            }
        }
        List<Integer> ans = new ArrayList<>();
        for (int i = m - 1; i >= 0; --i) {
            ans.add(k);
            k = pre[i][k];
        }
        Collections.reverse(ans);
        return ans;
    }
}

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class Solution {
public:
    vector<int> mostSimilar(int n, vector<vector<int>>& roads, vector<string>& names, vector<string>& targetPath) {
        vector<int> g[n];
        for (auto& r : roads) {
            int a = r[0], b = r[1];
            g[a].push_back(b);
            g[b].push_back(a);
        }
        int m = targetPath.size();
        int f[m][n];
        int pre[m][n];
        memset(f, 0x3f, sizeof(f));
        memset(pre, -1, sizeof(pre));
        for (int j = 0; j < n; ++j) {
            f[0][j] = targetPath[0] != names[j];
        }
        for (int i = 1; i < m; ++i) {
            for (int j = 0; j < n; ++j) {
                for (int k : g[j]) {
                    int t = f[i - 1][k] + (targetPath[i] != names[j]);
                    if (t < f[i][j]) {
                        f[i][j] = t;
                        pre[i][j] = k;
                    }
                }
            }
        }
        int k = 0;
        int mi = 1 << 30;
        for (int j = 0; j < n; ++j) {
            if (f[m - 1][j] < mi) {
                mi = f[m - 1][j];
                k = j;
            }
        }
        vector<int> ans(m);
        for (int i = m - 1; ~i; --i) {
            ans[i] = k;
            k = pre[i][k];
        }
        return ans;
    }
};

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func mostSimilar(n int, roads [][]int, names []string, targetPath []string) []int {
    g := make([][]int, n)
    for _, r := range roads {
        a, b := r[0], r[1]
        g[a] = append(g[a], b)
        g[b] = append(g[b], a)
    }
    m := len(targetPath)
    const inf = 1 << 30
    f := make([][]int, m)
    pre := make([][]int, m)
    for i := range f {
        f[i] = make([]int, n)
        pre[i] = make([]int, n)
        for j := range f[i] {
            f[i][j] = inf
            pre[i][j] = -1
        }
    }
    for j, s := range names {
        if targetPath[0] != s {
            f[0][j] = 1
        } else {
            f[0][j] = 0
        }
    }
    for i := 1; i < m; i++ {
        for j := 0; j < n; j++ {
            for _, k := range g[j] {
                t := f[i-1][k]
                if targetPath[i] != names[j] {
                    t++
                }
                if t < f[i][j] {
                    f[i][j] = t
                    pre[i][j] = k
                }
            }
        }
    }
    mi, k := inf, 0
    for j := 0; j < n; j++ {
        if f[m-1][j] < mi {
            mi = f[m-1][j]
            k = j
        }
    }
    ans := make([]int, m)
    for i := m - 1; i >= 0; i-- {
        ans[i] = k
        k = pre[i][k]
    }
    return ans
}

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function mostSimilar(
    n: number,
    roads: number[][],
    names: string[],
    targetPath: string[],
): number[] {
    const g: number[][] = Array.from({ length: n }, () => []);
    for (const [a, b] of roads) {
        g[a].push(b);
        g[b].push(a);
    }
    const m = targetPath.length;
    const f = Array.from({ length: m }, () => Array.from({ length: n }, () => Infinity));
    const pre: number[][] = Array.from({ length: m }, () => Array.from({ length: n }, () => -1));
    for (let j = 0; j < n; ++j) {
        f[0][j] = names[j] === targetPath[0] ? 0 : 1;
    }
    for (let i = 1; i < m; ++i) {
        for (let j = 0; j < n; ++j) {
            for (const k of g[j]) {
                const t = f[i - 1][k] + (names[j] === targetPath[i] ? 0 : 1);
                if (t < f[i][j]) {
                    f[i][j] = t;
                    pre[i][j] = k;
                }
            }
        }
    }
    let k = 0;
    let mi = Infinity;
    for (let j = 0; j < n; ++j) {
        if (f[m - 1][j] < mi) {
            mi = f[m - 1][j];
            k = j;
        }
    }
    const ans: number[] = Array(m).fill(0);
    for (let i = m - 1; ~i; --i) {
        ans[i] = k;
        k = pre[i][k];
    }
    return ans;
}

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