2307. Check for Contradictions in Equations 🔒

Description

You are given a 2D array of strings equations and an array of real numbers values, where equations[i] = [A_i, B_i] and values[i] means that A_i / B_i = values[i].

Determine if there exists a contradiction in the equations. Return true if there is a contradiction, or false otherwise.

Note:

When checking if two numbers are equal, check that their absolute difference is less than 10^-5.
The testcases are generated such that there are no cases targeting precision, i.e. using double is enough to solve the problem.

Example 1:

Input: equations = [["a","b"],["b","c"],["a","c"]], values = [3,0.5,1.5]
Output: false
Explanation:
The given equations are: a / b = 3, b / c = 0.5, a / c = 1.5
There are no contradictions in the equations. One possible assignment to satisfy all equations is:
a = 3, b = 1 and c = 2.

Example 2:

Input: equations = [["le","et"],["le","code"],["code","et"]], values = [2,5,0.5]
Output: true
Explanation:
The given equations are: le / et = 2, le / code = 5, code / et = 0.5
Based on the first two equations, we get code / et = 0.4.
Since the third equation is code / et = 0.5, we get a contradiction.

Constraints:

1 <= equations.length <= 100
equations[i].length == 2
1 <= A_i.length, B_i.length <= 5
A_i, B_i consist of lowercase English letters.
equations.length == values.length
0.0 < values[i] <= 10.0
values[i] has a maximum of 2 decimal places.

Solutions

Solution 1: Weighted Union-Find

First, we convert the strings into integers starting from $0$. Then, we traverse all the equations, map the two strings in each equation to the corresponding integers $a$ and $b$. If these two integers are not in the same set, we merge them into the same set and record the weights of the two integers, which is the ratio of $a$ to $b$. If these two integers are in the same set, we check whether their weights satisfy the equation. If not, we return true.

The time complexity is $O(n \times \log n)$ or $O(n \times \alpha(n))$, and the space complexity is $O(n)$. Here, $n$ is the number of equations.

Similar problems:

399. Evaluate Division

Python3JavaC++GoTypeScript

class Solution:
    def checkContradictions(
        self, equations: List[List[str]], values: List[float]
    ) -> bool:
        def find(x: int) -> int:
            if p[x] != x:
                root = find(p[x])
                w[x] *= w[p[x]]
                p[x] = root
            return p[x]

        d = defaultdict(int)
        n = 0
        for e in equations:
            for s in e:
                if s not in d:
                    d[s] = n
                    n += 1
        p = list(range(n))
        w = [1.0] * n
        eps = 1e-5
        for (a, b), v in zip(equations, values):
            a, b = d[a], d[b]
            pa, pb = find(a), find(b)
            if pa != pb:
                p[pb] = pa
                w[pb] = v * w[a] / w[b]
            elif abs(v * w[a] - w[b]) >= eps:
                return True
        return False

class Solution {
    private int[] p;
    private double[] w;

    public boolean checkContradictions(List<List<String>> equations, double[] values) {
        Map<String, Integer> d = new HashMap<>();
        int n = 0;
        for (var e : equations) {
            for (var s : e) {
                if (!d.containsKey(s)) {
                    d.put(s, n++);
                }
            }
        }
        p = new int[n];
        w = new double[n];
        for (int i = 0; i < n; ++i) {
            p[i] = i;
            w[i] = 1.0;
        }
        final double eps = 1e-5;
        for (int i = 0; i < equations.size(); ++i) {
            int a = d.get(equations.get(i).get(0)), b = d.get(equations.get(i).get(1));
            int pa = find(a), pb = find(b);
            double v = values[i];
            if (pa != pb) {
                p[pb] = pa;
                w[pb] = v * w[a] / w[b];
            } else if (Math.abs(v * w[a] - w[b]) >= eps) {
                return true;
            }
        }
        return false;
    }

    private int find(int x) {
        if (p[x] != x) {
            int root = find(p[x]);
            w[x] *= w[p[x]];
            p[x] = root;
        }
        return p[x];
    }
}

class Solution {
public:
    bool checkContradictions(vector<vector<string>>& equations, vector<double>& values) {
        unordered_map<string, int> d;
        int n = 0;
        for (auto& e : equations) {
            for (auto& s : e) {
                if (!d.count(s)) {
                    d[s] = n++;
                }
            }
        }
        vector<int> p(n);
        iota(p.begin(), p.end(), 0);
        vector<double> w(n, 1.0);
        function<int(int)> find = [&](int x) -> int {
            if (p[x] != x) {
                int root = find(p[x]);
                w[x] *= w[p[x]];
                p[x] = root;
            }
            return p[x];
        };
        for (int i = 0; i < equations.size(); ++i) {
            int a = d[equations[i][0]], b = d[equations[i][1]];
            double v = values[i];
            int pa = find(a), pb = find(b);
            if (pa != pb) {
                p[pb] = pa;
                w[pb] = v * w[a] / w[b];
            } else if (fabs(v * w[a] - w[b]) >= 1e-5) {
                return true;
            }
        }
        return false;
    }
};

func checkContradictions(equations [][]string, values []float64) bool {
    d := make(map[string]int)
    n := 0

    for _, e := range equations {
        for _, s := range e {
            if _, ok := d[s]; !ok {
                d[s] = n
                n++
            }
        }
    }

    p := make([]int, n)
    for i := range p {
        p[i] = i
    }

    w := make([]float64, n)
    for i := range w {
        w[i] = 1.0
    }

    var find func(int) int
    find = func(x int) int {
        if p[x] != x {
            root := find(p[x])
            w[x] *= w[p[x]]
            p[x] = root
        }
        return p[x]
    }
    for i, e := range equations {
        a, b := d[e[0]], d[e[1]]
        v := values[i]

        pa, pb := find(a), find(b)
        if pa != pb {
            p[pb] = pa
            w[pb] = v * w[a] / w[b]
        } else if v*w[a]-w[b] >= 1e-5 || w[b]-v*w[a] >= 1e-5 {
            return true
        }
    }

    return false
}

function checkContradictions(equations: string[][], values: number[]): boolean {
    const d: { [key: string]: number } = {};
    let n = 0;

    for (const e of equations) {
        for (const s of e) {
            if (!(s in d)) {
                d[s] = n;
                n++;
            }
        }
    }

    const p: number[] = Array.from({ length: n }, (_, i) => i);
    const w: number[] = Array.from({ length: n }, () => 1.0);

    const find = (x: number): number => {
        if (p[x] !== x) {
            const root = find(p[x]);
            w[x] *= w[p[x]];
            p[x] = root;
        }
        return p[x];
    };

    for (let i = 0; i < equations.length; i++) {
        const a = d[equations[i][0]];
        const b = d[equations[i][1]];
        const v = values[i];

        const pa = find(a);
        const pb = find(b);

        if (pa !== pb) {
            p[pb] = pa;
            w[pb] = (v * w[a]) / w[b];
        } else if (Math.abs(v * w[a] - w[b]) >= 1e-5) {
            return true;
        }
    }

    return false;
}

2307. Check for Contradictions in Equations 🔒

Description

Solutions

Solution 1: Weighted Union-Find

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