feat: add cache

Author: jtr109

min_cost_climbing_stairs/src/lib.rs

@@ -1,16 +1,22 @@
 pub struct Solution {}
 
 impl Solution {
-    fn min_cost_to_step(cost: &Vec<i32>, i: usize) -> i32 {
+    fn min_cost_to_step(cost: &Vec<i32>, cache: &mut Vec<Option<i32>>, i: usize) -> i32 {
         if i < 2 {
             return 0;
         }
-        (Self::min_cost_to_step(cost, i - 1) + cost[i - 1])
-            .min(Self::min_cost_to_step(cost, i - 2) + cost[i - 2])
+        if let Some(res) = cache[i] {
+            return res;
+        }
+        let res = (Self::min_cost_to_step(cost, cache, i - 1) + cost[i - 1])
+            .min(Self::min_cost_to_step(cost, cache, i - 2) + cost[i - 2]);
+        cache[i] = Some(res);
+        res
     }
 
     pub fn min_cost_climbing_stairs(cost: Vec<i32>) -> i32 {
-        Self::min_cost_to_step(&cost, cost.len())
+        let mut cache = vec![None; cost.len() + 1];
+        Self::min_cost_to_step(&cost, &mut cache, cost.len())
     }
 }