Runtime: 3 ms (Top 100.0%) | Memory: 3.00 MB (Top 86.96%)

Author: AnasImloul

scripts/algorithms/L/Longest Arithmetic Subsequence of Given Difference/Longest Arithmetic Subsequence of Given Difference.rs

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+// Runtime: 3 ms (Top 100.0%) | Memory: 3.00 MB (Top 86.96%)
+
+const RANGE_MIN: i32 = -10_000;
+const RANGE_MAX: i32 = 10_000;
+
+impl Solution {
+    pub fn longest_subsequence(arr: Vec<i32>, difference: i32) -> i32 {
+        let range = (RANGE_MAX - RANGE_MIN + 1) as usize;
+        fn offset(i: i32) -> Option<usize> {
+            if RANGE_MIN <= i && i <= RANGE_MAX {
+                Some((i - RANGE_MIN) as usize)
+            } else {
+                None
+            }
+        }
+        /// "Length when last seen"; longest subseq when we last saw that arr[i] value
+        let mut lwls = vec![0_i32; range];
+        let mut best = 1;
+        for &a in arr.iter().rev() {
+            let old = offset(a + difference).map(|i| lwls[i]).unwrap_or(0);
+            let new_idx = offset(a).unwrap();  // safety: problem constraints
+            let len = lwls[new_idx].max(old + 1);
+            lwls[new_idx] = len;
+            best = best.max(len);
+        }
+        best
+    }
+}