2022-02-26 Daily-Challenge

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Today I have done leetcode's February LeetCoding Challenge with cpp.

February LeetCoding Challenge 26

Description

Shortest Path Visiting All Nodes

You have an undirected, connected graph of n nodes labeled from 0 to n - 1. You are given an array graph where graph[i] is a list of all the nodes connected with node i by an edge.

Return the length of the shortest path that visits every node. You may start and stop at any node, you may revisit nodes multiple times, and you may reuse edges.

Example 1:

img

Input: graph = [[1,2,3],[0],[0],[0]]
Output: 4
Explanation: One possible path is [1,0,2,0,3]

Example 2:

img

Input: graph = [[1],[0,2,4],[1,3,4],[2],[1,2]]
Output: 4
Explanation: One possible path is [0,1,4,2,3]

Constraints:

  • n == graph.length
  • 1 <= n <= 12
  • 0 <= graph[i].length < n
  • graph[i] does not contain i.
  • If graph[a] contains b, then graph[b] contains a.
  • The input graph is always connected.

Solution

pair<int, int> getState(int state) {
  int visited = ((1 << 12) - 1) & state;
  state >>= 12;
  int current;
  for(int i = 0; i < 12; ++i) {
    if((1 << i) & state) current = i;
  }
  return {current, visited};
}
inline constexpr int genState(int current, int visited) {
  return (1 << (current + 12)) | visited;
}
class Solution {
public:
  int shortestPathLength(vector<vector<int>>& graph) {
    int len = graph.size();
    const int TARGET = (1 << len) - 1;
    queue<int> q;
    unordered_set<int> states;
    for(int i = 0; i < len; ++i) {
      int state = genState(i, (1 << i));
      q.push(state);
      states.insert(state);
    }
    int answer = 0;
    while(q.size()) {
      int sz = q.size();
      for(int _ = 0; _ < sz; ++_) {
        auto [current, visited] = getState(q.front());
        q.pop();
        if(visited == TARGET) return answer;
        for(auto nxt : graph[current]) {
          int state = genState(nxt, visited | (1 << nxt));
          if(states.count(state))continue;
          states.insert(state);
          q.push(state);
        }
      }
      answer += 1;
    }
    return -1;
  }
};

// Accepted
// 51/51 cases passed (101 ms)
// Your runtime beats 49.34 % of cpp submissions
// Your memory usage beats 59.24 % of cpp submissions (16.3 MB)
Algorithm