20250526 finished.

src/problem/mod.rs

@@ -676,3 +676,5 @@ mod p3068_find_the_maximum_sum_of_node_values;
 mod p2942_find_words_containing_character;
 
 mod p2131_longest_palindrome_by_concatenating_two_letter_words;
+
+mod p1857_largest_color_value_in_a_directed_graph;

src/problem/p1857_largest_color_value_in_a_directed_graph.rs

@@ -0,0 +1,98 @@
+/**
+ * [1857] Largest Color Value in a Directed Graph
+ */
+pub struct Solution {}
+
+// submission codes start here
+use std::collections::{HashMap, VecDeque};
+use std::iter::FromIterator;
+
+impl Solution {
+    pub fn largest_path_value(colors: String, edges: Vec<Vec<i32>>) -> i32 {
+        let colors: Vec<usize> = colors.bytes().map(|x| (x - b'a') as usize).collect();
+        let mut adjacency_matrix = vec![vec![]; colors.len()];
+        // 入度节点
+        let mut in_degrees = vec![0; colors.len()];
+
+        for edge in edges.iter() {
+            let start = edge[0] as usize;
+            let end = edge[1] as usize;
+
+            adjacency_matrix[start].push(end);
+            in_degrees[end] += 1;
+        }
+
+        // 使用拓扑排序判断是否有环
+        // 同时获得一个拓扑序列表
+        let mut queue = VecDeque::from_iter(in_degrees.iter().enumerate().filter_map(|(i, v)| {
+            if *v == 0 {
+                Some(i)
+            } else {
+                None
+            }
+        }));
+        let mut topology_list = vec![];
+
+        while let Some(head) = queue.pop_front() {
+            topology_list.push(head);
+            for &next in adjacency_matrix[head].iter() {
+                in_degrees[next] -= 1;
+
+                if in_degrees[next] == 0 {
+                    queue.push_back(next);
+                }
+            }
+        }
+
+        if in_degrees.iter().any(|x| *x != 0) {
+            return -1;
+        }
+
+        // dp[i][c]表示从节点i开始路径上颜色为c的计数
+        // 颜色只能是小写字母
+        let mut dp = vec![vec![0; 26]; topology_list.len()];
+        let mut result = HashMap::new();
+
+        for &node in topology_list.iter().rev() {
+            let c = colors[node];
+
+            for &next in adjacency_matrix[node].iter() {
+                for i in 0..26 {
+                    dp[node][i] = dp[node][i].max(dp[next][i]);
+                }
+
+                dp[node][c] = dp[node][c].max(dp[next][c] + 1);
+                let entry = result.entry(c).or_insert(0);
+                *entry = dp[node][c].max(*entry);
+            }
+
+            if adjacency_matrix[node].is_empty() {
+                dp[node][c] = 1;
+            }
+        }
+
+        result.values().max().map_or_else(|| 1, |x| *x)
+    }
+}
+
+// submission codes end
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_1857() {
+        assert_eq!(
+            3,
+            Solution::largest_path_value(
+                "abaca".to_string(),
+                vec![vec![0, 1], vec![0, 2], vec![2, 3], vec![3, 4]]
+            )
+        );
+        assert_eq!(
+            -1,
+            Solution::largest_path_value("a".to_string(), vec![vec![0, 0]])
+        );
+    }
+}