add: #230 climbing stairs

Author: sukyoungshin

climbing-stairs/sukyoungshin.ts

@@ -0,0 +1,42 @@
+// 1번풀이 (hashMap)
+function climbStairs1(n: number): number {
+  const dp: Record<number, number> = {
+    1: 1,
+    2: 2,
+  };
+
+  for (let i = 3; i <= n; i++) {
+    dp[i] = dp[i - 1] + dp[i - 2];
+  }
+
+  return dp[n];
+};
+
+// 2번풀이 (배열)
+function climbStairs2(n: number): number {
+  const dp = [0, 1, 2]; // dp[1] = 1, dp[2] = 2
+
+  for (let i = 3; i <= n; i++) {
+    dp[i] = dp[i - 1] + dp[i - 2];
+  }
+
+  return dp[n];
+};
+
+// 3번풀이
+// 불필요한 배열 전체 저장을 제거하고, 필요한 값만 2개만 유지
+function climbStairs(n: number): number {
+  if (n <= 2) return n;
+
+  let prev1 = 1; // dp[i - 2]
+  let prev2 = 2; // dp[i - 1]
+
+  for (let i = 3; i <= n; i++) {
+    const current = prev1 + prev2;
+    prev1 = prev2;
+    prev2 = current;
+  }
+
+  return prev2;
+};
+