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95.不同的二叉搜索树-ii.js
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95.不同的二叉搜索树-ii.js
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/*
* @lc app=leetcode.cn id=95 lang=javascript
*
* [95] 不同的二叉搜索树 II
*/
// @lc code=start
/**
* Definition for a binary tree node.
* function TreeNode(val, left, right) {
* this.val = (val===undefined ? 0 : val)
* this.left = (left===undefined ? null : left)
* this.right = (right===undefined ? null : right)
* }
*/
/**
* @param {number} n
* @return {TreeNode[]}
*
* @description 当一个二叉树的父节点为 i 时他的左节点为 0~i-1,右节点为
* i+1 ~ n 所以可以用递归取每一个节点左右节点组合
*/
var generateTrees = function (n) {
if (n == 0) return [];
function generateTreesNode(left, right) {
if (left > right) {
// 左侧比右侧大,不符合二叉树要求所以返回[null]供后续遍历取值
return [null]
}
if (left === right) return [new TreeNode(left)];
let res = [];
for (let i = left; i <= right; i++) {
const leftNodes = generateTreesNode(left, i - 1)
const rightNodes = generateTreesNode(i + 1, right)
for (let leftKey of leftNodes) {
for (let rightKey of rightNodes) {
let root = new TreeNode(i);
root.left = leftKey;
root.right = rightKey;
res.push(root)
}
}
}
return res;
}
return generateTreesNode(1, n)
};
// @lc code=end