week4;按题型分类

70works/week4/daily/bfs/day27_minMutation.js

+var minMutation = function(start, end, bank) {
+    let used = new Set(bank);
+    let level = 0;
+    if(!used.has(end)) return -1;
+    let queue = [];
+    queue.push([start, 0]);
+    let gene = ['A', 'C', 'G', 'T'];
+    while(queue.length > 0) {
+        let [currStr, count] = queue.shift();
+        if(currStr === end) return count;
+        for(let i =0; i < currStr.length; i++) {
+            for(let j =0; j <gene.length; j++) {
+                if(currStr[i] !== gene[j]) {
+                    let d = currStr.slice(0, i) + gene[j] +currStr.slice(i+1);
+                    console.error(`d: ${d}`);
+                    if(used.has(d)) {
+                        queue.push([d, count+1]);
+                        used.delete(d);
+                    }
+                }
+            }
+        }
+    }
+    return -1;
+};
+let start = "AACCGGTT";
+let end = "AACCGGTA";
+let bank = ["AACCGGTA"];
+minMutation(start, end, bank);
+// console.log(nums);

70works/week4/daily/day23_47permutation-ii.js

+var permute = function(nums) {
+    let visited = [];
+    let path = [];
+    let res=[];
+    if (nums.length < 0){
+        return res;
+    }
+    //sort用法弄错，这题重点就是要先排序！！！
+    nums.sort((a,b) => a - b);
+
+    const dfs = (visited, path) => {
+        if (path.length == nums.length) {
+            console.error(`遍历完的路径${path}`);
+            res.push(path.slice());
+        }
+        for(let i =0; i< nums.length; i++) {
+            if (visited[i]) continue;
+            if(i>0 && nums[i] === nums[i-1] && !visited[i-1]) continue;
+            path.push(nums[i]);
+            console.error(`开始遍历的路径${path}`);
+            visited[i] = true;
+            dfs(visited.slice(), path.slice());
+            path.pop();
+            console.error(`开始回溯的路径${path}`);
+            visited[i] = false;
+        }
+    }
+    dfs(visited, path);
+    return res;
+};
+let nums = [3,3,0,3];
+let res = permute(nums);
+console.log(res);

70works/week4/work/树的遍历/day26_860_binary_tree_level_order_traversal.cpp

+/**
+/**
+ * Definition for a binary tree node.
+ * struct TreeNode {
+ *     int val;
+ *     TreeNode *left;
+ *     TreeNode *right;
+ *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
+ * };
+ */
+class Solution {
+public:
+    vector<vector<int>> levelOrder(TreeNode* root) {
+        queue<TreeNode*>qu;
+        vector<vector<int>>res;
+        if(root == nullptr) {
+             return res;
+        }
+        qu.push(root);
+        while(!qu.empty()) {
+            int size = qu.size();
+            vector<int> tmp;
+            for(int i =0; i < size; i++) {
+                
+            TreeNode* node = qu.front();
+            qu.pop();
+            tmp.push_back(node->val);
+            if(node->left != nullptr) {
+                qu.push(node->left);
+            }
+            if(node->right != nullptr) {
+                qu.push(node->right);
+            }
+            }
+            res.push_back(tmp);
+
+        }
+        return res;
+    }
+};
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70works/week4/work/第四周学习总结.md

+### 第四周学习总结
+### 第四周学习总结
+
+#### 深度优先搜索、广度优先搜索
+
+- 深度优先搜索
+  - 一般用递归
+- 广度优先搜索
+  - 可以用递归或者非递归，递归一般是使用队列；非递归则是要使用栈来模拟
+  - 题目总结：
+    - 2叉树层序遍历，基因序列
+
+#### 贪心算法
+
+- 贪心算法是一种从局部找最优解的算法，它不可以回溯。
+- 特殊的求解方法，从前往后贪心或者从后往前贪心；
+- 题目总结：
+  - 柠檬水找零
+  - 买卖股票的最佳时机ii
+
+#### 二分查找
+
+- 寻找一个中间值，从中间值分为左右两边去求解，以此类推。
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70works/week4/work/贪心/day23_122best_time_to_buy_and_sell_stock_ii.js

+/**思路:贪心
+/**思路:贪心
+ * @param {number[]} prices
+ * @return {number}
+ */
+var maxProfit = function(prices) {
+    let benifit =0;
+    for(let i = 0; i < prices.length; i++) {
+        let j = i-1;
+        let tmp = prices[i] - prices[j];
+        if(tmp> 0) {
+            benifit += tmp;
+        }
+    }
+    return benifit;
+};

70works/week4/work/贪心/day24_860_lemonade-change.cpp

+class Solution {
+class Solution {
+public:
+    bool lemonadeChange(vector<int>& bills) {
+        int size = bills.size();
+        int five = 0;
+        int ten =0;
+        for(int i = 0;　i<size;i++) {
+            if(bills[i] == 5) {
+                five ++;
+            } else if(bills[i] == 10) {
+                if (five == 0) {
+                    return false;
+                }
+                five--;
+                ten++;
+            } else {
+                if (five >0 && ten >0) {
+                    five--;
+                    ten--;
+                } else if(five >= 3) {
+                    five -=3;
+                } else {
+                    return false;
+                }
+            }
+        }
+        return true;
+    }
+};
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