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1345. Jump Game IV

Description

Given an array of integers arr, you are initially positioned at the first index of the array.

In one step you can jump from index i to index:

  • i + 1 where: i + 1 < arr.length.
  • i - 1 where: i - 1 >= 0.
  • j where: arr[i] == arr[j] and i != j.

Return the minimum number of steps to reach the last index of the array.

Notice that you can not jump outside of the array at any time.

 

Example 1:

Input: arr = [100,-23,-23,404,100,23,23,23,3,404]
Output: 3
Explanation: You need three jumps from index 0 --> 4 --> 3 --> 9. Note that index 9 is the last index of the array.

Example 2:

Input: arr = [7]
Output: 0
Explanation: Start index is the last index. You do not need to jump.

Example 3:

Input: arr = [7,6,9,6,9,6,9,7]
Output: 1
Explanation: You can jump directly from index 0 to index 7 which is last index of the array.

 

Constraints:

  • 1 <= arr.length <= 5 * 104
  • -108 <= arr[i] <= 108

Solutions

Solution 1

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class Solution:
    def minJumps(self, arr: List[int]) -> int:
        idx = defaultdict(list)
        for i, v in enumerate(arr):
            idx[v].append(i)
        q = deque([(0, 0)])
        vis = {0}
        while q:
            i, step = q.popleft()
            if i == len(arr) - 1:
                return step
            v = arr[i]
            step += 1
            for j in idx[v]:
                if j not in vis:
                    vis.add(j)
                    q.append((j, step))
            del idx[v]
            if i + 1 < len(arr) and (i + 1) not in vis:
                vis.add(i + 1)
                q.append((i + 1, step))
            if i - 1 >= 0 and (i - 1) not in vis:
                vis.add(i - 1)
                q.append((i - 1, step))

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class Solution {
    public int minJumps(int[] arr) {
        Map<Integer, List<Integer>> idx = new HashMap<>();
        int n = arr.length;
        for (int i = 0; i < n; ++i) {
            idx.computeIfAbsent(arr[i], k -> new ArrayList<>()).add(i);
        }
        Deque<int[]> q = new LinkedList<>();
        Set<Integer> vis = new HashSet<>();
        vis.add(0);
        q.offer(new int[] {0, 0});
        while (!q.isEmpty()) {
            int[] e = q.pollFirst();
            int i = e[0], step = e[1];
            if (i == n - 1) {
                return step;
            }
            int v = arr[i];
            ++step;
            for (int j : idx.getOrDefault(v, new ArrayList<>())) {
                if (!vis.contains(j)) {
                    vis.add(j);
                    q.offer(new int[] {j, step});
                }
            }
            idx.remove(v);
            if (i + 1 < n && !vis.contains(i + 1)) {
                vis.add(i + 1);
                q.offer(new int[] {i + 1, step});
            }
            if (i - 1 >= 0 && !vis.contains(i - 1)) {
                vis.add(i - 1);
                q.offer(new int[] {i - 1, step});
            }
        }
        return -1;
    }
}

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class Solution {
public:
    int minJumps(vector<int>& arr) {
        unordered_map<int, vector<int>> idx;
        int n = arr.size();
        for (int i = 0; i < n; ++i) idx[arr[i]].push_back(i);
        queue<pair<int, int>> q;
        q.emplace(0, 0);
        unordered_set<int> vis;
        vis.insert(0);
        while (!q.empty()) {
            auto e = q.front();
            q.pop();
            int i = e.first, step = e.second;
            if (i == n - 1) return step;
            int v = arr[i];
            ++step;
            if (idx.count(v)) {
                for (int j : idx[v]) {
                    if (!vis.count(j)) {
                        vis.insert(j);
                        q.emplace(j, step);
                    }
                }
                idx.erase(v);
            }
            if (i + 1 < n && !vis.count(i + 1)) {
                vis.insert(i + 1);
                q.emplace(i + 1, step);
            }
            if (i - 1 >= 0 && !vis.count(i - 1)) {
                vis.insert(i - 1);
                q.emplace(i - 1, step);
            }
        }
        return -1;
    }
};

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func minJumps(arr []int) int {
    idx := map[int][]int{}
    for i, v := range arr {
        idx[v] = append(idx[v], i)
    }
    vis := map[int]bool{0: true}
    type pair struct{ idx, step int }
    q := []pair{{0, 0}}
    for len(q) > 0 {
        e := q[0]
        q = q[1:]
        i, step := e.idx, e.step
        if i == len(arr)-1 {
            return step
        }
        step++
        for _, j := range idx[arr[i]] {
            if !vis[j] {
                vis[j] = true
                q = append(q, pair{j, step})
            }
        }
        delete(idx, arr[i])
        if i+1 < len(arr) && !vis[i+1] {
            vis[i+1] = true
            q = append(q, pair{i + 1, step})
        }
        if i-1 >= 0 && !vis[i-1] {
            vis[i-1] = true
            q = append(q, pair{i - 1, step})
        }
    }
    return -1
}

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