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🤖 Daily Challenge: Problem #2976 #37

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20 changes: 20 additions & 0 deletions include/leetcode/problems/minimum-cost-to-convert-string-i.h
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#include "leetcode/core.h"

namespace leetcode {
namespace problem_2976 {

using Func = std::function<long long(string, string, vector<char>&, vector<char>&, vector<int>&)>;

class MinimumCostToConvertStringISolution : public SolutionBase<Func> {
public:
//! 2976. Minimum Cost to Convert String I
//! https://leetcode.com/problems/minimum-cost-to-convert-string-i/
long long minimumCost(string source, string target,
vector<char>& original, vector<char>& changed,
vector<int>& cost);

MinimumCostToConvertStringISolution();
};

} // namespace problem_2976
} // namespace leetcode
140 changes: 140 additions & 0 deletions src/leetcode/problems/minimum-cost-to-convert-string-i.cpp
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#include "leetcode/problems/minimum-cost-to-convert-string-i.h"

namespace leetcode {
namespace problem_2976 {

// 策略1：Floyd-Warshall 算法计算所有字符对之间的最小转换成本
// 时间复杂度：O(26^3 + n + m)，其中 n 是 source 长度，m 是转换规则数量
// 空间复杂度：O(26^2) = O(1)
static long long solution1(string source, string target,
vector<char>& original, vector<char>& changed,
vector<int>& cost) {
const long long INF = 1e18;
const int ALPHABET = 26;
vector<vector<long long>> dist(ALPHABET, vector<long long>(ALPHABET, INF));

// 初始化对角线为 0（相同字符转换成本为 0）
for (int i = 0; i < ALPHABET; ++i) {
dist[i][i] = 0;
}

// 根据给定的转换规则更新直接转换成本
int m = original.size();
for (int i = 0; i < m; ++i) {
int u = original[i] - 'a';
int v = changed[i] - 'a';
long long w = cost[i];
if (w < dist[u][v]) {
dist[u][v] = w;
}
}

// Floyd-Warshall 算法计算所有对最短路径
for (int k = 0; k < ALPHABET; ++k) {
for (int i = 0; i < ALPHABET; ++i) {
if (dist[i][k] == INF) continue;
for (int j = 0; j < ALPHABET; ++j) {
if (dist[k][j] == INF) continue;
long long newDist = dist[i][k] + dist[k][j];
if (newDist < dist[i][j]) {
dist[i][j] = newDist;
}
}
}
}

// 计算将 source 转换为 target 的总成本
long long totalCost = 0;
int n = source.size();
for (int i = 0; i < n; ++i) {
if (source[i] == target[i]) {
continue;
}
int u = source[i] - 'a';
int v = target[i] - 'a';
if (dist[u][v] == INF) {
return -1;
}
totalCost += dist[u][v];
}
return totalCost;
}

// 策略2：对每个字符运行 Dijkstra 算法
// 时间复杂度：O(26 * (26 log 26 + m)) + O(n)
// 空间复杂度：O(26^2 + m)
static long long solution2(string source, string target,
vector<char>& original, vector<char>& changed,
vector<int>& cost) {
const long long INF = 1e18;
const int ALPHABET = 26;

// 构建邻接表
vector<vector<pair<int, long long>>> adj(ALPHABET);
int m = original.size();
for (int i = 0; i < m; ++i) {
int u = original[i] - 'a';
int v = changed[i] - 'a';
long long w = cost[i];
adj[u].emplace_back(v, w);
}

// 预计算所有字符对的最短距离
vector<vector<long long>> dist(ALPHABET, vector<long long>(ALPHABET, INF));

// 对每个字符运行 Dijkstra 算法
for (int start = 0; start < ALPHABET; ++start) {
priority_queue<pair<long long, int>, vector<pair<long long, int>>, greater<pair<long long, int>>> pq;
dist[start][start] = 0;
pq.emplace(0, start);

while (!pq.empty()) {
auto [d, u] = pq.top();
pq.pop();

if (d != dist[start][u]) continue;

for (auto& [v, w] : adj[u]) {
long long newDist = d + w;
if (newDist < dist[start][v]) {
dist[start][v] = newDist;
pq.emplace(newDist, v);
}
}
}
}

// 计算总成本
long long totalCost = 0;
int n = source.size();
for (int i = 0; i < n; ++i) {
if (source[i] == target[i]) {
continue;
}
int u = source[i] - 'a';
int v = target[i] - 'a';
if (dist[u][v] == INF) {
return -1;
}
totalCost += dist[u][v];
}
return totalCost;
}

MinimumCostToConvertStringISolution::MinimumCostToConvertStringISolution() {
setMetaInfo({.id = 2976,
.title = "Minimum Cost to Convert String I",
.url = "https://leetcode.com/problems/minimum-cost-to-convert-string-i/"});
registerStrategy("Floyd-Warshall", solution1);
registerStrategy("Dijkstra per character", solution2);
}

long long MinimumCostToConvertStringISolution::minimumCost(
string source, string target,
vector<char>& original, vector<char>& changed,
vector<int>& cost) {
return getSolution()(source, target, original, changed, cost);
}

} // namespace problem_2976
} // namespace leetcode
123 changes: 123 additions & 0 deletions test/leetcode/problems/minimum-cost-to-convert-string-i.cpp
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#include "leetcode/problems/minimum-cost-to-convert-string-i.h"

#include "gtest/gtest.h"

namespace leetcode {
namespace problem_2976 {

class MinimumCostToConvertStringITest : public ::testing::TestWithParam<string> {
protected:
void SetUp() override { solution.setStrategy(GetParam()); }

MinimumCostToConvertStringISolution solution;
};

TEST_P(MinimumCostToConvertStringITest, Example1) {
string source = "abcd";
string target = "acbe";
vector<char> original = {'a', 'b', 'c', 'c', 'e', 'd'};
vector<char> changed = {'b', 'c', 'b', 'e', 'b', 'e'};
vector<int> cost = {2, 5, 5, 1, 2, 20};
long long expected = 28;
long long result = solution.minimumCost(source, target, original, changed, cost);
EXPECT_EQ(expected, result);
}

TEST_P(MinimumCostToConvertStringITest, Example2) {
string source = "aaaa";
string target = "bbbb";
vector<char> original = {'a', 'c'};
vector<char> changed = {'c', 'b'};
vector<int> cost = {1, 2};
long long expected = 12;
long long result = solution.minimumCost(source, target, original, changed, cost);
EXPECT_EQ(expected, result);
}

TEST_P(MinimumCostToConvertStringITest, Example3) {
string source = "abcd";
string target = "abce";
vector<char> original = {'a'};
vector<char> changed = {'e'};
vector<int> cost = {10000};
long long expected = -1;
long long result = solution.minimumCost(source, target, original, changed, cost);
EXPECT_EQ(expected, result);
}

TEST_P(MinimumCostToConvertStringITest, SameString) {
string source = "hello";
string target = "hello";
vector<char> original = {'a', 'b'};
vector<char> changed = {'b', 'c'};
vector<int> cost = {1, 2};
long long expected = 0;
long long result = solution.minimumCost(source, target, original, changed, cost);
EXPECT_EQ(expected, result);
}

TEST_P(MinimumCostToConvertStringITest, DirectConversion) {
string source = "abc";
string target = "def";
vector<char> original = {'a', 'b', 'c'};
vector<char> changed = {'d', 'e', 'f'};
vector<int> cost = {10, 20, 30};
long long expected = 10 + 20 + 30;
long long result = solution.minimumCost(source, target, original, changed, cost);
EXPECT_EQ(expected, result);
}

TEST_P(MinimumCostToConvertStringITest, IndirectConversion) {
string source = "aa";
string target = "bb";
vector<char> original = {'a', 'c'};
vector<char> changed = {'c', 'b'};
vector<int> cost = {5, 7};
// 转换路径：a -> c (5) + c -> b (7) = 12 per character
long long expected = 24;
long long result = solution.minimumCost(source, target, original, changed, cost);
EXPECT_EQ(expected, result);
}

TEST_P(MinimumCostToConvertStringITest, MultipleEdgesSamePair) {
string source = "a";
string target = "b";
vector<char> original = {'a', 'a', 'a'};
vector<char> changed = {'b', 'b', 'b'};
vector<int> cost = {100, 10, 1};
// 应该选择最小的成本 1
long long expected = 1;
long long result = solution.minimumCost(source, target, original, changed, cost);
EXPECT_EQ(expected, result);
}

TEST_P(MinimumCostToConvertStringITest, Unreachable) {
string source = "a";
string target = "b";
vector<char> original = {'a', 'c'};
vector<char> changed = {'c', 'd'};
vector<int> cost = {1, 2};
// 没有从 a 到 b 的路径
long long expected = -1;
long long result = solution.minimumCost(source, target, original, changed, cost);
EXPECT_EQ(expected, result);
}

TEST_P(MinimumCostToConvertStringITest, SelfLoop) {
string source = "a";
string target = "a";
vector<char> original = {'a'};
vector<char> changed = {'a'};
vector<int> cost = {100};
// 相同字符不需要转换，成本为 0
long long expected = 0;
long long result = solution.minimumCost(source, target, original, changed, cost);
EXPECT_EQ(expected, result);
}

INSTANTIATE_TEST_SUITE_P(
LeetCode, MinimumCostToConvertStringITest,
::testing::ValuesIn(MinimumCostToConvertStringISolution().getStrategyNames()));

} // namespace problem_2976
} // namespace leetcode