【leetcode】96. Unique Binary Search Trees

动态规划问题入门，分解成左右两颗子树。
Given n, how many structurally unique BST’s (binary search trees) that store values 1…n?

For example,
Given n = 3, there are a total of 5 unique BST’s.

   1         3     3      2      1    \       /     /      / \      \     3     2     1      1   3      2    /     /       \                 \   2     1         2                 3

/** * @param {number} n * @return {number} */var numTrees = function(n) {    var dp = new Array(n);    dp[0]=1;    dp[1]=1;    if(n==1){        return 1;    }    for(var i=2;i<=n;i++){        dp[i]=0;        for(var j=0;j<i;j++){            dp[i] += dp[j]*dp[i-j-1];        }    }    return dp[n];};