20240629 Finished

src/problem/mod.rs

@@ -161,3 +161,4 @@ mod p207_course_schedule;
 mod p210_course_schedule_ii;
 mod p909_snakes_and_ladders;
 mod p433_minimum_genetic_mutation;
+mod p127_word_ladder;

src/problem/p127_word_ladder.rs

@@ -0,0 +1,175 @@
+/**
+ * [127] Word Ladder
+ */
+pub struct Solution {}
+
+// submission codes start here
+use std::collections::HashSet;
+
+impl Solution {
+    pub fn ladder_length(begin_word: String, end_word: String, word_list: Vec<String>) -> i32 {
+        let mut start = usize::MAX;
+        let mut start_found = false;
+        let mut end_found = false;
+        let mut end = usize::MAX;
+
+        for (i, word) in word_list.iter().enumerate() {
+            if *word == begin_word {
+                start_found = true;
+                start = i;
+                break;
+            }
+        } 
+
+        let mut neighbors = vec![HashSet::new(); word_list.len()];
+
+        // 构建邻接矩阵
+        for i in 0..word_list.len() {
+            for j in 1..word_list.len() {
+                if Self::is_one_char(&word_list[i], &word_list[j]) {
+                    neighbors[i].insert(j);
+                    neighbors[j].insert(i);
+                }
+            }
+
+            if word_list[i] == end_word {
+                end_found = true;
+                end = i;
+            }
+
+            if !start_found {
+                if Self::is_one_char(&word_list[i], &begin_word) {
+                    start = i;
+                }
+            }
+        }
+
+        if !end_found {
+            return 0;
+        }
+
+        // 如果开始和结束相同
+        // 则必然是跳了一步
+        if start == end {
+            return 2; 
+        }
+
+        let mut result = i32::MAX;
+
+        // dijkstra算法
+        let mut distances = vec![i32::MAX; word_list.len()];
+            let mut flags = vec![false; word_list.len()];
+            distances[start] = 0;
+            flags[start] = true;
+            for &i in &neighbors[start] {
+                distances[i] = 1;
+            }
+
+            for _ in 1..word_list.len() {
+                let mut min = i32::MAX;
+                let mut next = 0;
+
+                for i in 0..word_list.len() {
+                    if !flags[i] && distances[i] < min {
+                        min = distances[i];
+                        next = i;
+                    }
+                }
+
+                flags[next] = true;
+                if next == end {
+                    result = result.min(min);
+                    break;
+                }
+
+                for &i in &neighbors[next] {
+                    if !flags[i] && min + 1 < distances[i] {
+                        distances[i] = min + 1;
+                    }
+                }
+            }
+
+        if result == i32::MAX {
+            0
+        } else {
+            if start_found {
+                result + 1
+            } else {
+                result + 2
+            }
+        }
+    }
+
+    fn is_one_char(a: &String, b: &String) -> bool {
+        let mut one_char = false;
+
+        for (c1, c2) in a.chars().zip(b.chars()) {
+            if c1 != c2 {
+                if one_char {
+                    return false;
+                } else {
+                    one_char = true
+                }
+            }
+        }
+
+        one_char
+    }
+}
+
+// submission codes end
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_127() {
+        assert_eq!(
+            Solution::ladder_length(
+                "hit".to_owned(),
+                "cog".to_owned(),
+                vec![
+                    "hot".to_owned(),
+                    "dot".to_owned(),
+                    "dog".to_owned(),
+                    "lot".to_owned(),
+                    "log".to_owned(),
+                    "cog".to_owned()
+                ]
+            ),
+            5
+        );
+        
+        assert_eq!(Solution::ladder_length("a".to_owned(), "c".to_owned(), vec![
+            "a".to_owned(),
+            "b".to_owned(),
+            "c".to_owned()
+        ]), 2);
+        
+        assert_eq!(Solution::ladder_length("a".to_owned(), "c".to_owned(), vec![
+            "c".to_owned()
+        ]), 2);
+        
+        assert_eq!(
+            Solution::ladder_length(
+                "hot".to_owned(),
+                "dog".to_owned(),
+                vec![
+                    "hot".to_owned(),
+                    "dot".to_owned(),
+                    "dog".to_owned(),
+                ]
+            ),
+            3
+        );
+
+        assert_eq!(Solution::ladder_length("lost".to_owned(), "cost".to_owned(), vec![
+            "most".to_owned(),
+            "fist".to_owned(),
+            "lost".to_owned(),
+            "cost".to_owned(),
+            "fish".to_owned()
+        ]), 2);
+    }
+}