feat: 2025-10-31打卡

96.unique-binary-search-trees.java

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+/*
+ * @lc app=leetcode id=96 lang=java
+ *
+ * [96] Unique Binary Search Trees
+ */
+
+// @lc code=start
+class Solution {
+    /**
+     * dp[n] = dp[n-1] + dp[1]+dp[n-2]
+     * 
+     * @param n
+     * @return
+     */
+    public int numTrees(int n) {
+        int[] dp = new int[n+1];
+        for(int i=1; i<=n; i++) {
+            dp[i] = 0;
+        }
+        dp[1] = 1;
+        for(int i=2; i<=n; i++) {
+            for(int j=0; j<=i-1;j++) {
+                int left = j>0?dp[j]:1;
+                int right = i-1-j>0?dp[i-1-j]:1;
+                dp[i] += left*right;
+            }
+        }
+        return dp[n];
+    }
+}
+// @lc code=end
+