并查集、带权并查集

并查集介绍

今天刷leetcode碰到一个带权重的并查集，记录一下

题目：399. 除法求值

class Solution {
public:
    int findf(vector<int>& f, vector<double>& w, int x) {
        if (f[x] != x) {
            int father = findf(f, w, f[x]);
            w[x] = w[x] * w[f[x]];
            f[x] = father;
        }
        return f[x];
    }

    void merge(vector<int>& f, vector<double>& w, int x, int y, double val) {
        int fx = findf(f, w, x);
        int fy = findf(f, w, y);
        f[fx] = fy;
        w[fx] = val * w[y] / w[x];
    }

    vector<double> calcEquation(vector<vector<string>>& equations, vector<double>& values, vector<vector<string>>& queries) {
        int nvars = 0;
        unordered_map<string, int> variables;

        int n = equations.size();
        for (int i = 0; i < n; i++) {
            if (variables.find(equations[i][0]) == variables.end()) {
                variables[equations[i][0]] = nvars++;
            }
            if (variables.find(equations[i][1]) == variables.end()) {
                variables[equations[i][1]] = nvars++;
            }
        }
        vector<int> f(nvars);
        vector<double> w(nvars, 1.0);
        for (int i = 0; i < nvars; i++) {
            f[i] = i;
        }

        for (int i = 0; i < n; i++) {
            int va = variables[equations[i][0]], vb = variables[equations[i][1]];
            merge(f, w, va, vb, values[i]);
        }
        vector<double> ret;
        for (const auto& q: queries) {
            double result = -1.0;
            if (variables.find(q[0]) != variables.end() && variables.find(q[1]) != variables.end()) {
                int ia = variables[q[0]], ib = variables[q[1]];
                int fa = findf(f, w, ia), fb = findf(f, w, ib);
                if (fa == fb) {
                    result = w[ia] / w[ib];
                }
            }
            ret.push_back(result);
        }
        return ret;
    }
};

作者：LeetCode-Solution
链接：https://leetcode-cn.com/problems/evaluate-division/solution/chu-fa-qiu-zhi-by-leetcode-solution-8nxb/
来源：力扣（LeetCode）
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