LeetCode:111.二叉树的最小深度
解题思路求最小深度，考虑使用广度优先遍历。在广度优先遍历过程中，遇到叶子节点，停止遍历，返回节点层级。
解题步骤广度优先遍历整棵树，并记录每个节点的层级。遇到叶子节点，返回节点层级，停止遍历。
//dfs
var minDepth = function(root) {if (!root) return 0;function dfs(node) {if (!node.left && !node.right) return 1; // 叶子节点，返回深度1let leftDepth = Infinity, rightDepth = Infinity;if (node.left) leftDepth = dfs(node.left);if (node.right) rightDepth = dfs(node.right);return Math.min(leftDepth, rightDepth) + 1;}return dfs(root);
};var minDepth = function(root) {if (!root) return 0;let queue = [[root, 1]];while(queue.length) {let [n,length]=queue.shift();if(!n.left&&!n.right) return length;if(n.left){queue.push([n.left,length+1])}if(n.right){queue.push([n.right,length+1])}}
};
// time 2ms space 83.99mb O(n)var minDepth = function(root) {if (!root) return 0;let queue = [{n:root,length:1}];while(queue.length) {let {n,length}=queue.shift();if(!n.left&&!n.right) return length;if(n.left){queue.push({n:n.left,length:length+1})}if(n.right){queue.push({n:n.right,length:length+1})}}
};
// time 4ms space 83.96mb O(n)// time 7ms space 85.56mb
var minDepth = function(root) {if (!root) return 0;let s=Symbol('root')let map=new Map()map.set(s,{n:root,length:1})let keylet n,lengthwhile(map.size>0) {key=Array.from(map.keys())[0]n=map.get(key).nlength=map.get(key).lengthmap.delete(key);if(!n.left&&!n.right) return length;if(n.left){map.set(Symbol(),{n:n.left,length:length+1})}if(n.right){map.set(Symbol(),{n:n.right,length:length+1})}}
};//time 10ms space 83.66mb
var minDepth = function(root) {if (!root) return 0;let s=Symbol('root')let map=new Map()let weakMap=new WeakMap()weakMap.set(s,{n:root,length:1})map.set(s,weakMap)let keylet n,lengthwhile(map.size>0) {key=Array.from(map.keys())[0];n=map.get(key).get(key).n;length=map.get(key).get(key).length;map.delete(key);weakMap.delete(key);if(!n.left&&!n.right) return length;if(n.left){let l=Symbol();map.set(l,weakMap.set(l,{n:n.left,length:length+1}))}if(n.right){let r=Symbol();map.set(r,weakMap.set(r,{n:n.right,length:length+1}))}}map=nullweakMap=null
};//time 14ms space 86mb
var minDepth = function(root) {if (!root) return 0;let minDepth = Infinity;function preorder(node, depth) {if (!node) return;// If it's a leaf nodeif (!node.left && !node.right) {minDepth = Math.min(minDepth, depth);}preorder(node.left, depth + 1);preorder(node.right, depth + 1);}preorder(root, 1);return minDepth;
};//只用map 和 一个symbol 不通过....error simple
//可能只能3个symbol----
var minDepth = function(root) {if (!root) return 0;let s = Symbol('node');let map = new Map();map.set(s, { node: root, depth: 1 });while (map.size > 0) {let { node, depth } = map.get(s);map.delete(s);if (!node.left && !node.right) {return depth;}if (node.left) {map.set(s, { node: node.left, depth: depth + 1 });}if (node.right) {// If left child exists, we need to process it firstif (!map.has(s)) {map.set(s, { node: node.right, depth: depth + 1 });}}}
};6/3
