update 322

Author: fishercoder1534

src/main/java/com/fishercoder/solutions/_322.java

@@ -7,14 +7,31 @@ public static class Solution1 {
          * credit: https://leetcode.com/problems/coin-change-2/discuss/99212/Knapsack-problem-Java-solution-with-thinking-process-O(nm)-Time-and-O(m)-Space
          */
         public int coinChange(int[] coins, int amount) {
-            int[] dp = new int[amount + 1];
-            dp[0] = 1;
+            if (amount < 1) {
+                return 0;
+            }
+            return coinChange(coins, amount, new int[amount]);
+        }
+
+        private int coinChange(int[] coins, int rem, int[] count) {
+            if (rem < 0) {
+                return -1;
+            }
+            if (rem == 0) {
+                return 0;
+            }
+            if (count[rem - 1] != 0) {
+                return count[rem - 1];
+            }
+            int min = Integer.MAX_VALUE;
             for (int coin : coins) {
-                for (int i = coin; i <= amount; i++) {
-                    dp[i] += dp[i - coin];
+                int res = coinChange(coins, rem - coin, count);
+                if (res >= 0 && res < min) {
+                    min = 1 + res;
                 }
             }
-            return dp[amount];
+            count[rem - 1] = (min == Integer.MAX_VALUE) ? -1 : min;
+            return count[rem - 1];
         }
     }