技術標籤：刷題

難度：困難。
跟昨天的每日一題 1631. 最小體力消耗路徑 一樣的。

並查集 正確解法：

class UnionfindSet{
public:
    vector<int> parents;

    UnionfindSet(int n):parents(vector<int> (n)){
        for(int i = 0; i < n; i++){
            parents[i] = i;
        }
    }

    int find_root(int x){
        return parents[
 
x] == x?parents[x]:parents[x] = find_root(parents[x]);
    }

    void merge(int x, int y){
        int rootx = find_root(x);
        int rooty = find_root(y);
        if(rootx != rooty){
            parents[rooty] = rootx;
        }
    }

    bool connect(int x, int y){
        int rootx = find_root
 
(x);
        int rooty = find_root(y);
        return rootx == rooty;
    }

};


class Solution {
public:
    int swimInWater(vector<vector<int>>& grid) {
        int n = grid.size();
        vector<tuple<int, int, int>> points;
        for(int i = 0; i < n; i++){
            for
 
(int j = 0; j < n; j++){
                int start = i * n + j;
                if(i < n - 1){
                    int weight = grid[i][j] > grid[i + 1][j]?grid[i][j]:grid[i + 1][j];
                    points.emplace_back(start, start + n, weight);
                }
                if(j < n - 1){
                    int weight = grid[i][j] > grid[i][j + 1]?grid[i][j]:grid[i][j + 1];
                    points.emplace_back(start, start + 1, weight);
                }
            }
        }

        sort(points.begin(), points.end(),[](const auto& p1, const auto& p2){
            auto&& [x1, y1, v1] = p1;
            auto&& [x2, y2, v2] = p2;
            return v1 < v2;
        });

        UnionfindSet uf(n * n);
        for(const auto [x, y, v] : points){
            uf.merge(x, y);
            if(uf.connect(0, n * n - 1)){
                return v;
            }
        }
        return 0;
    }
};