刷题日记Day6 | BST计算合法BST

Posted 2021-12-15 结构化思维wz

文章目录

• • 96.不同的二叉搜索树

96.不同的二叉搜索树

解答：

class Solution 
    // 备忘录
    int[][] memo;

    int numTrees(int n) 
        // 备忘录的值初始化为 0
        memo = new int[n + 1][n + 1];
        return count(1, n);
    

    int count(int lo, int hi) 
        if (lo > hi) return 1;
        // 查备忘录
        if (memo[lo][hi] != 0) 
            return memo[lo][hi];
        

        int res = 0;
        for (int mid = lo; mid <= hi; mid++) 
            int left = count(lo, mid - 1);
            int right = count(mid + 1, hi);
            res += left * right;
        
        // 将结果存入备忘录
        memo[lo][hi] = res;

        return res;