20250126 finished.

src/problem/mod.rs

@@ -454,3 +454,5 @@ mod p2920_maximum_points_after_collecting_coins_from_all_nodes;
 mod p2944_minimum_number_of_coins_for_fruits;
 
 mod p2412_minimum_money_required_before_transactions;
+
+mod p40_combination_sum_ii;

src/problem/p40_combination_sum_ii.rs

@@ -0,0 +1,100 @@
+/**
+ * [40] Combination Sum II
+ */
+pub struct Solution {}
+
+// submission codes start here
+use std::collections::HashMap;
+use std::iter::FromIterator;
+
+impl Solution {
+    pub fn combination_sum2(candidates: Vec<i32>, target: i32) -> Vec<Vec<i32>> {
+        let mut frequency_map = HashMap::new();
+
+        for c in candidates {
+            let entry = frequency_map.entry(c).or_insert(0);
+            *entry += 1;
+        }
+
+        // (number, count)
+        let mut candidates = Vec::from_iter(frequency_map.into_iter());
+        candidates.sort();
+
+        let mut path = vec![];
+        let mut result = vec![];
+
+        Self::dfs(&candidates, 0, target, &mut path, &mut result);
+
+        result
+    }
+
+    fn dfs(
+        candidates: &Vec<(i32, i32)>,
+        pos: usize,
+        rest: i32,
+        path: &mut Vec<i32>,
+        result: &mut Vec<Vec<i32>>,
+    ) {
+        if rest == 0 {
+            result.push(path.clone());
+            return;
+        }
+
+        if pos >= candidates.len() || rest < candidates[pos].0 {
+            return;
+        }
+
+        // 不选择pos
+        Self::dfs(candidates, pos + 1, rest, path, result);
+
+        // 选择pos
+        // 能够选择pos最多的次数
+        let count = candidates[pos].1.min(rest / candidates[pos].0);
+        for i in 1..=count {
+            path.push(candidates[pos].0);
+            Self::dfs(
+                candidates,
+                pos + 1,
+                rest - candidates[pos].0 * i,
+                path,
+                result,
+            );
+        }
+
+        // dfs结束弹出
+        for _ in 1..=count {
+            path.pop();
+        }
+    }
+}
+
+// submission codes end
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use std::collections::HashSet;
+
+    fn vec_equal_helper(expect: Vec<Vec<i32>>, actual: Vec<Vec<i32>>) {
+        let set: HashSet<Vec<i32>> = HashSet::from_iter(expect.into_iter());
+
+        assert_eq!(set.len(), actual.len());
+
+        for array in actual {
+            assert!(set.contains(&array));
+        }
+    }
+
+    #[test]
+    fn test_40() {
+        vec_equal_helper(
+            vec![vec![1, 1, 6], vec![1, 2, 5], vec![1, 7], vec![2, 6]],
+            Solution::combination_sum2(vec![10, 1, 2, 7, 6, 1, 5], 8),
+        );
+
+        vec_equal_helper(
+            vec![vec![1, 2, 2], vec![5]],
+            Solution::combination_sum2(vec![2, 5, 2, 1, 2], 5),
+        );
+    }
+}