#273 Unique Paths - 공간 복잡도 O(n)으로 줄임

Author: forest000014

unique-paths/forest000014.java

@@ -1,21 +1,23 @@
 /*
 Time Complexity: O(m * n)
-Space Complexity: O(m * n)
+Space Complexity: O(n)
 */
 class Solution {
     public int uniquePaths(int m, int n) {
-        int[][] dp = new int[m][n];
+        int[] dp = new int[n];
 
         for (int i = 0; i < n; i++) {
-            dp[0][i] = 1;
+            dp[i] = 1;
         }
+
         for (int i = 1; i < m; i++) {
-            dp[i][0] = 1;
+            int prev = dp[0];
             for (int j = 1; j < n; j++) {
-                dp[i][j] = dp[i - 1][j] + dp[i][j - 1];
+                dp[j] += prev;
+                prev = dp[j];
             }
         }
 
-        return dp[m - 1][n - 1];
+        return dp[n - 1];
     }
 }