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int minDisNode(vector<bool> &visited, vector<int> &dis) {
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    int min_v = INT_MAX, min_i = -1;;
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    for(int j = 0;j < dis.size();j++) {
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        if (!visited[j] && dis[j] < min_v) {
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            min_v = dis[j];
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            min_i = j;
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        }
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    }
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    return min_i;
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}
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int networkDelayTime(vector<vector<int>>& times, int N, int K) {
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    if (times.size() == 0 || N==0 || K <= 0) return -1;
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    //build graph;
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    vector<vector<int>> graph(N, vector<int>(N, INT_MAX));
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    for(auto &t: times) {
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        graph[t[0]-1][t[1]-1] = t[2];
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    }
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    K--;
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    vector<int> dis(N, INT_MAX);
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    vector<bool> visited(N, false);
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    visited[K] = true;
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    for(int i = 0;i < dis.size(); i++) {
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        dis[i] = graph[K][i];
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    }
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    dis[K] = 0;
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    for(int i = 1;i < N; i++) {
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        // find a unvisited node which dis is min
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        int j = minDisNode(visited, dis);
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        if (j == -1) return -1;
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        visited[j] = true;
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        for(int k = 0;k < dis.size(); k++) {
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            if (graph[j][k] != INT_MAX) {
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                dis[k] = min(dis[k], dis[j] + graph[j][k]);
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            }
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        }
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    }
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    int res = 0;
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    for(int i = 0;i < N;i++) {
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        if (dis[i] != INT_MAX)
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            res = max(res, dis[i]);
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    }
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    return res;
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}