feat: 2025-10-31打卡

121.best-time-to-buy-and-sell-stock.java

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+/*
+ * @lc app=leetcode id=121 lang=java
+ *
+ * [121] Best Time to Buy and Sell Stock
+ */
+
+// @lc code=start
+class Solution {
+    public int maxProfit(int[] prices) {
+        if(prices == null || prices.length == 0) {
+            return 0;
+        }   
+        int min = prices[0], profit = 0;
+        for(int i=1; i<prices.length; i++) {
+            profit = Math.max(profit, prices[i] - min);
+            min = Math.min(min, prices[i]);
+        }
+        return profit;
+    }
+}
+// @lc code=end
+

123.best-time-to-buy-and-sell-stock-iii.java

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+/*
+ * @lc app=leetcode id=123 lang=java
+ *
+ * [123] Best Time to Buy and Sell Stock III
+ */
+
+// @lc code=start
+class Solution {
+    public int maxProfit(int[] prices) {
+        int[] ldp = new int[prices.length];
+        int[] rdp = new int[prices.length];
+        for(int i=0; i<ldp.length; i++) {
+            ldp[i] = 0;
+            rdp[i] = 0;
+        }
+        int lmin = prices[0], maxProfit=0;
+        for(int i=1; i<ldp.length; i++) {
+            maxProfit = Math.max(maxProfit, prices[i]-lmin);
+            lmin = Math.min(lmin, prices[i]);
+            ldp[i] = maxProfit;
+        }
+        int rmax = prices[prices.length-1];
+        maxProfit = 0;
+        for(int i=rdp.length-2; i>=0; i--) {
+            maxProfit = Math.max(maxProfit, rmax - prices[i]);
+            rmax = Math.max(rmax, prices[i]);
+            rdp[i] = maxProfit;
+        }
+        int profit = ldp[ldp.length-1];
+        for(int i=0; i<ldp.length-1; i++) {
+            profit = Math.max(profit, ldp[i] + rdp[i+1]);
+        }
+        return profit;
+    }
+}
+// @lc code=end
+

152.maximum-product-subarray.java

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+/*
+ * @lc app=leetcode id=152 lang=java
+ *
+ * [152] Maximum Product Subarray
+ */
+
+// @lc code=start
+class Solution {
+    public int maxProduct(int[] nums) {
+        int min = 1, max = 1, r = nums[0], curMax, curMin;
+        for(int i = 0; i< nums.length; i++) {
+            if(nums[i] == 0) {
+                max = min = 0;
+                r = Math.max(r, 0);
+            } else if(nums[i] > 0) {
+                curMax = Math.max(nums[i], max*nums[i]);
+                curMin = Math.min(nums[i], min*nums[i]);
+                max = curMax;
+                min = curMin;
+            } else {
+                curMax = Math.max(min * nums[i], nums[i]);
+                curMin = Math.min(max*nums[i], nums[i]);
+                max = curMax;
+                min = curMin;
+            }
+            r = Math.max(max, r);
+        }
+        return r;
+    }
+}
+// @lc code=end
+