2021刷题打卡

今天开始，每日刷题打卡，加油鸭！

6/7/21

1880. Check if Word Equals Summation of Two Words, 直接用String加，String转Integer：Integer.valueOf()可以直接去0啊, Time: O(N), Space: O(N)
1119. Remove Vowels from a String, Time: O(N), Space: O(N)
1480. Running Sum of 1d Array, presum, Time: O(N), Space: O(1)
1108. Defanging an IP Address, StringBuilder比String快, StringBuilder.toString(), Time: O(N), Space: O(N)
1672. Richest Customer Wealth, Time: O(M*N), Space: O(1)
1512. Number of Good Pairs, 普通解法, 嵌套Loop,Time: O(N^2), Space: O(1); 用Map记录前面nums出现过的次数n, res+=n就是合法的pair, 每次更新map中的次数n++, 第一次出现n = 1， Time: O(N), Space: O(N), 空间换时间
1431. Kids With the Greatest Number of Candies, Time: O(N), Space: O(N)
1470. Shuffle the Array, 双指针: Time: O(N), Space: O(N);  偶数位放X, i对应i / 2, 奇数位放Y, i对应n + i / 2, 记得要new新的res array，不然原数组顺序会受影响, Time: O(N), Space: O(N)

苏格拉底的猫 发表于 2021-6-10 15:50
楼主有兴趣加入我们不

好呀，你们是有刷题群吗？

6/10

709. To Lower Case, 只有大写需要转, Time: O(N), Space: O(N)
1684. Count the Number of Consistent Strings, Time: O(N*M), Space: O(N)
1290. Convert Binary Number in a Linked List to Integer, 用sum记录当前和, 每次sum *= 2, 再考虑是否需要+1, Time: O(N), Space: O(1)
1469. Find All The Lonely Nodes, 两种解法: BFS和DFS, 只往下层找永远有parent, 不用特殊处理, Time: O(N), Space: O(N)
1816. Truncate Sentence, Time: O(N), Space: O(N)
1213. Intersection of Three Sorted Arrays, Three pointers, 嵌套while挪指针更快一点, Time: O(N), Space: O(1)
1844. Replace All Digits with Characters, Time: O(N), Space: O(N)
1732. Find the Highest Altitude, Time: O(N), Space: O(1)
1315. Sum of Nodes with Even-Valued Grandparent, 两种解法, BFS和DFS, 在DFS时, 仔细想想怎样可以剪更多枝, Time: O(N), Space: O(N)
1302. Deepest Leaves Sum, 两种解法, BFS和DFS, BFS时不需要先找max深度再求和, 每层算一个sum, 外层用res记录每层的和, 最后一定是最后一层的! DFS时, 先traverse一遍找到max depth, 再traverse求和, Time: O(N), Space: O(N)
1609. Even Odd Tree, BFS, 每层遍历时, 用一个prev变量记录当前节点的上一个节点的值, Time: O(N), Space: O(N)
1367. Linked List in Binary Tree, DFS, 定义helper函数, 用来检查从当前节点开始的子树是否valid, 返回root开头的有没有 || 主函数(左子树) || 主函数(右子树)

6/8/21

771. Jewels and Stones, 用Set记录jewels, 依次check石头, 也可以用数组记录jewels，因为只有英文字母知道总数, Time: O(N), Space: O(N)
1281. Subtract the Product and Sum of Digits of an Integer, Time: O(N), Space: O(1)
1603. Design Parking System, 用数组记录每种spaces, carType - 1就是对应space中的index, Time: O(1), Space: O(N)
1165. Single-Row Keyboard, 用Map记录<character, index>, 减完记得Math.abs(), Time: O(N), Space: O(N)
1528. Shuffle String, char[] temp转String，不可以直接temp.toString(), 要用String.valueOf(temp), Time: O(N), Space: O(N)
1720. Decode XORed Array, bit manipulation, X ^ Y = Z => X ^ Z = Y && Y ^ Z = X; X ^ X = 0, Time: O(N), Space: O(N)
1486. XOR Operation in an Array, Time: O(N), Space: O(1)
1221. Split a String in Balanced Strings, 用两个变量分别记录L和R的个数, 一旦相等res++, 中间不需要重置变量值, 再次相等时就是valid, Time: O(N), Space: O(1)
1389. Create Target Array in the Given Order, list.add(index, val), List转int array, 直接用loop转, Time: O(N), Space: O(N)
1678. Goal Parser Interpretation, Time: O(N), Space: O(N)
1773. Count Items Matching a Rule, 判断String是否相等不可以直接用==, 要用str1.equals(str2), Time: O(N), Space: O(1)
1313. Decompress Run-Length Encoded List, Time: O(N), Space: O(N)

6/9/21

938. Range Sum of BST, 三种方法, 分治 & traverse & 非递归, 遇到树上非递归的解法多想想stack, 递归就是通过stack实现, 处理子树的时候, 不同方法条件略有不同想清楚, Time: O(N), Space: O(N)
1832. Check if the Sentence Is Pangram, Time: O(N), Space: O(N)
1662. Check If Two String Arrays are Equivalent, Time: O(N), Space: O(N)
760. Find Anagram Mappings, Time: O(N), Space: O(N)
1859. Sorting the Sentence, 遇到需要在i的位置插入值得时候用array比较合适, String.trim(), Time: O(N), Space: O(N)
1614. Maximum Nesting Depth of the Parentheses, 用count记录深度, (的话count ++, )的话count --， 每次max, The depth of any character in the VPS is the ( number of left brackets before it ) - ( number of right brackets before it ), Time: O(N), Space: O(1)
1656. Design an Ordered Stream, Time: O(N), Space: O(1)
1342. Number of Steps to Reduce a Number to Zero, Time: O(logN), Space: O(1)

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6/11
1837. Sum of Digits in Base K, Time: O(N), Space: O(1)

6/12

832. Flipping an Image, x ^= 1, 每位取反, Time: O(M * N), Space: O(1)
1704. Determine if String Halves Are Alike, str = str.toLowerCase(), Time: O(N), Space: O(1)
804. Unique Morse Code Words, String[] dict = new String[]{"x", "y", "z"}, Time: O(N), Space: O(N)
1295. Find Numbers with Even Number of Digits, 转String或者计算多少位, Time: O(N), Space: O(1)
1572. Matrix Diagonal Sum, 主对角线: mat[i][i], 辅对角线: mat[i][n - i - 1], 排除掉重合的点, 在加辅对角线上的点时, 检查i != j就行, Time: O(N), Space:O(1)

6/13
344. Reverse String, 双指针, Time: O(N), Space:O(1)
977. Squares of a Sorted Array, 双指针, 最大的可能性在原数组两端, 从后往前放, Time: O(N), Space: O(N)
1047. Remove All Adjacent Duplicates In String, Stack, Time: O(N), Space: O(N)
728. Self Dividing Numbers, Time is NlogM, N: 多少个数, M: 最大数有多少位, 假设valid的Integer, logM可以视为常数Time: O(N), Space: O(N)
1207. Unique Number of Occurrences, Time: O(N), Space: O(N)
1085. Sum of Digits in the Minimum Number, Time: O(N), Space: O(1)

求楼主拉 最近也准备刷题了

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