Leetcode 797 - All Paths From Source to Target

題目

Problem#

graph

給你一個 n 個點的有向無環圖(DAG)，問你可不可以找到所有從 0 到 n-1 的路徑。

想法#

• 時間複雜度: $\mathcal{O}(n+m)$ (n個點，m條邊)
• 空間複雜度: $\mathcal{O}(n)$

AC Code#

DFS + backtracking

Copy

class Solution {
public:
    vector<vector<int>> G;
    vector<int> p;
    vector<bool> vis;
    vector<vector<int>> ans;
 
    void solve(int fr, int to)
    {
        if(fr == to)
        {
            ans.push_back(p);
            return;
        }
 
        for(int i : G[fr])
        {
            if(!vis[i])
            {
                vis[i] = true;
                p.push_back(i);
                solve(i, to);
                p.pop_back();
                vis[i] = false;
            }
        }
    }
 
    vector<vector<int>> allPathsSourceTarget(vector<vector<int>>& graph) {
        G = graph;
        int n = G.size();
        vis.resize(n);
 
        vis[0] = true;
        p.push_back(0);
        solve(0, n-1);
        return ans;
    }
};

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