modify code

MCA算法突击课/第03期/mca_09/Code05_CoinChange.java

@@ -7,22 +7,73 @@ package 第03期.mca_09;
 // 测试链接 : https://leetcode.cn/problems/coin-change-ii/
 public class Code05_CoinChange {
 
-	public static int change(int aim, int[] arr) {
-		if (arr == null || arr.length == 0 || aim < 0) {
+	public static int change1(int aim, int[] arr) {
+		return process1(arr, 0, aim);
+	}
+
+	public static int process1(int[] arr, int i, int j) {
+		if (j < 0) {
+			return 0;
+		}
+		if (i == arr.length) {
+			return j == 0 ? 1 : 0;
+		}
+		return process1(arr, i + 1, j) + process1(arr, i, j - arr[i]);
+	}
+
+	public static int change2(int aim, int[] arr) {
+		int n = arr.length;
+		int[][] dp = new int[n][aim + 1];
+		for (int i = 0; i < n; i++) {
+			for (int j = 0; j <= aim; j++) {
+				dp[i][j] = -1;
+			}
+		}
+		return process2(arr, 0, aim, dp);
+	}
+
+	public static int process2(int[] arr, int i, int j, int[][] dp) {
+		if (j < 0) {
 			return 0;
 		}
-		int N = arr.length;
-		int[][] dp = new int[N + 1][aim + 1];
-		dp[N][0] = 1;
-		for (int index = N - 1; index >= 0; index--) {
-			for (int rest = 0; rest <= aim; rest++) {
-				dp[index][rest] = dp[index + 1][rest];
-				if (rest - arr[index] >= 0) {
-					dp[index][rest] += dp[index][rest - arr[index]];
+		if (i == arr.length) {
+			return j == 0 ? 1 : 0;
+		}
+		if (dp[i][j] != -1) {
+			return dp[i][j];
+		}
+		int ans = process2(arr, i + 1, j, dp) + process2(arr, i, j - arr[i], dp);
+		dp[i][j] = ans;
+		return ans;
+	}
+
+	public static int change3(int aim, int[] arr) {
+		int n = arr.length;
+		int[][] dp = new int[n + 1][aim + 1];
+		dp[n][0] = 1;
+		for (int i = n - 1; i >= 0; i--) {
+			for (int j = 0; j <= aim; j++) {
+				dp[i][j] = dp[i + 1][j];
+				if (j - arr[i] >= 0) {
+					dp[i][j] += dp[i][j - arr[i]];
 				}
 			}
 		}
 		return dp[0][aim];
 	}
 
+	public static int change4(int aim, int[] arr) {
+		int n = arr.length;
+		int[] dp = new int[aim + 1];
+		dp[0] = 1;
+		for (int i = n - 1; i >= 0; i--) {
+			for (int j = 0; j <= aim; j++) {
+				if (j - arr[i] >= 0) {
+					dp[j] += dp[j - arr[i]];
+				}
+			}
+		}
+		return dp[aim];
+	}
+
 }