[122] 买卖股票的最佳时机 II

src/leecode/122.买卖股票的最佳时机-ii.java

@@ -0,0 +1,103 @@
+package leecode;/*
+ * @lc app=leetcode.cn id=122 lang=java
+ *
+ * [122] 买卖股票的最佳时机 II
+ */
+
+// @lc code=start
+class Solution {
+    //贪心算法
+    public int maxProfit(int[] prices) {
+        int len = prices.length;
+        if (len < 2) {
+            return 0;
+        }
+
+        int res = 0;
+        for (int i = 1; i < len; i++) {
+            int diff = prices[i] - prices[i - 1];
+            if (diff > 0) {
+                res += diff;
+            }
+        }
+        return res;
+    }
+    //动态规划
+    public int maxProfit2(int[] prices) {
+        int len = prices.length;
+        if (len < 2) {
+            return 0;
+        }
+
+        // 0：没有股票时的现金
+        // 1：持有股票时的现金
+        // 状态转移：0 → 1 → 0 → 1 → 0 → 1 → 0
+        int[][] dp = new int[len][2];
+
+        dp[0][0] = 0;
+        dp[0][1] = -prices[0];
+
+        for (int i = 1; i < len; i++) {
+            //今天未持有股票，昨天未持有或者昨天持有今天卖掉
+            dp[i][0] = Math.max(dp[i - 1][0], dp[i - 1][1] + prices[i]);
+            //今天持有股票，持有的是昨天的股票或者今天买入的股票
+            dp[i][1] = Math.max(dp[i - 1][1], dp[i - 1][0] - prices[i]);
+        }
+        return dp[len - 1][0];
+//        int[][] dp = new int[prices.length + 1][prices.length + 1];
+//        for (int i = 1; i <= prices.length; i++) {
+//            dp[prices.length][i] = prices[prices.length - 1];
+//        }
+//        for (int i = prices.length - 1; i >= 1; i--) {
+//            for (int j = 0; j < prices.length; j++) {
+//                int nextSellNoBuy = 0, nextSellBuy = 0, nextBuy = 0;
+//                //不交易
+//                int nextNoTrade = dp[i + 1][j];
+//                if (j == 0) {
+//                    nextBuy = -prices[i] + dp[i + 1][i];
+//                } else {
+//                    //卖了不买
+//                    nextSellNoBuy = prices[i] + dp[i + 1][0];
+//                    //卖了买
+//                    nextSellBuy = -prices[j] + dp[i + 1][i];
+//                }
+//                dp[i][j] = Math.max(Math.max(nextSellNoBuy, nextSellBuy), Math.max(nextBuy, nextNoTrade));
+//            }
+//        }
+//        return dp[1][0];
+//        return loop(prices, 0, -1);
+    }
+
+    //暴力递归
+    private int dfs(int[] prices, int index, int cur) {
+        if (index == prices.length - 1) {
+            if (cur != -1) {
+                //最后一天还持股，直接卖
+                return prices[index];
+            } else {
+                return 0;
+            }
+        }
+        int nextSellNoBuy = 0, nextSellBuy = 0, nextBuy = 0;
+        //不交易
+        int nextNoTrade = dfs(prices, index + 1, cur);
+        if (cur == -1) {
+            nextBuy = -prices[index] + dfs(prices, index + 1, index);
+        } else {
+            //卖了不买
+            nextSellNoBuy = prices[index] + dfs(prices, index + 1, -1);
+            //卖了买
+            nextSellBuy = -prices[cur] + dfs(prices, index + 1, index);
+        }
+        return Math.max(Math.max(nextNoTrade, nextBuy), Math.max(nextSellNoBuy, nextSellBuy));
+    }
+
+    public static void main(String[] args) {
+        int[] price = new int[]{1, 2, 3};
+        Solution solution = new Solution();
+        System.out.println(solution.maxProfit(price));
+    }
+
+}
+// @lc code=end
+

src/leecode/91.解码方法.java

@@ -7,7 +7,7 @@ package leecode;/*
 import java.util.Arrays;
 
 // @lc code=start test
-class Solution {
+class No91 {
     public int numDecodings(String s) {
         int[] dp = new int[s.length() + 1];
         Arrays.fill(dp, -1);
@@ -34,7 +34,7 @@ class Solution {
     }
 
     public static void main(String[] args) {
-        Solution solution = new Solution();
+        No91 solution = new No91();
         System.out.println(solution.numDecodings("0"));
     }
 }