0829学习

agile Posted on Aug 29 2023

面试 leetcode学习

-   除法求值-399
给你一个变量对数组 equations 和一个实数值数组 values 作为已知条件，其中 equations[i] = [Ai, Bi] 和 values[i] 共同表示等式 Ai / Bi = values[i] 。每个 Ai 或 Bi 是一个表示单个变量的字符串。
另有一些以数组 queries 表示的问题，其中 queries[j] = [Cj, Dj] 表示第 j 个问题，请你根据已知条件找出 Cj / Dj = ? 的结果作为答案。
返回 所有问题的答案 。如果存在某个无法确定的答案，则用 -1.0 替代这个答案。如果问题中出现了给定的已知条件中没有出现的字符串，也需要用 -1.0 替代这个答案。
注意：输入总是有效的。你可以假设除法运算中不会出现除数为 0 的情况，且不存在任何矛盾的结果。
注意：未在等式列表中出现的变量是未定义的，因此无法确定它们的答案。
示例 1：
输入：equations = [["a","b"],["b","c"]], values = [2.0,3.0], queries = [["a","c"],["b","a"],["a","e"],["a","a"],["x","x"]]
输出：[6.00000,0.50000,-1.00000,1.00000,-1.00000]
解释：
条件：a / b = 2.0, b / c = 3.0
问题：a / c = ?, b / a = ?, a / e = ?, a / a = ?, x / x = ?
结果：[6.0, 0.5, -1.0, 1.0, -1.0 ]
注意：x 是未定义的 => -1.0

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```C#
class Cell
{
    public string Str;
    public double Value;

public Cell(string str, double v)
    {
        Str = str;
        Value = v;
    }

public override bool Equals(object? obj)
    {
        if (obj is Cell c)
        {
            return c.Str == Str;
        }

return false;
    }
}

public double[] CalcEquation(IList<IList<string>> equations, double[] values, IList<IList<string>> queries)
{
    var visited = new List<string>();
    var info = new Dictionary<string, List<Cell>>();
    for (int i = 0; i < equations.Count; i++)
    {
        var t = equations[i];
        var key0 = t[0];
        var key1 = t[1];
        var v = values[i];
        __Add(info, key0, key1, v);
        __Add(info, key1, key0, 1 / v);
    }

foreach (var kv in info)
    {
        if (kv.Value.Count == 1)
        {
            var first = kv.Value.First();
        }
    }

var result = new double[queries.Count];
    Array.Fill(result, -1);
    var cache = new HashSet<string>();
    for (int i = 0; i < queries.Count; i++)
    {
        var t = queries[i];
        var key0 = t[0];
        var key1 = t[1];
        cache.Clear();
        __VisitedEquation(info, cache, key0, key1, result, i, 1);
    }

return result;
}

private void __VisitedEquation(Dictionary<string, List<Cell>> info,
    HashSet<string> cache, string src, string target, double[] result, int index, double value)
{
    if (cache.Contains(src))
    {
        return;
    }

cache.Add(src);

if (src == target && info.ContainsKey(src))
    {
        result[index] = value;
        return;
    }

if (info.TryGetValue(src, out var cells))
    {
        foreach (var cell in cells)
        {
            __VisitedEquation(info, cache, cell.Str, target, result, index, value * cell.Value);
        }
    }
}

private void __Add(Dictionary<string, List<Cell>> info, string key, string value, double v)
{
    if (!info.TryGetValue(key, out var list))
    {
        list = new List<Cell>();
        info[key] = list;
    }

var c = new Cell(value, v);
    if (!list.Contains(c))
    {
        list.Add(c);
    }
}

public double[] CalcEquation2(IList<IList<string>> equations, double[] values, IList<IList<string>> queries)
{
    var cache = new Dictionary<string, Dictionary<string, double>>();
    for (int i = 0; i < equations.Count; i++)
    {
        var t = equations[i];
        var v = values[i];
        var key0 = t[0];
        var key1 = t[1];
        __Add(cache, key0, key1, v);
        __Add(cache, key1, key0, 1 / v);
    }

return result;
}

private double __Dfs(Dictionary<string, Dictionary<string, double>> cache,
    Dictionary<string, HashSet<string>> visited, string source, string target, double value)
{
    if (source == target)
    {
        return value;
    }

foreach (var kvPair in cache[source])
    {
        var k = kvPair.Key;
        var v = kvPair.Value;
        if (!visited.TryGetValue(source, out var hashVisited))
        {
            hashVisited = new HashSet<string>();
            visited[source] = hashVisited;
        }

double temp = -1;
        if (hashVisited.Add(k))
        {
            temp = __Dfs(cache, visited, k, target, v);
        }

if (Math.Abs(temp + 1) > 0.01f && k != target)
        {
            return temp * v;
        }

if (k == target)
        {
            return temp;
        }
    }

return -1;
}

private void __Add(Dictionary<string, Dictionary<string, double>> info, string key, string value, double v)
{
    if (!info.TryGetValue(key, out var list))
    {
        list = new Dictionary<string, double>();
        info[key] = list;
    }

if (!list.ContainsKey(value))
    {
        list[value] = v;
    }
}
```
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