LeetCode 693 - Binary Number with Alternating Bits


https://leetcode.com/problems/binary-number-with-alternating-bits/description/
Given a positive integer, check whether it has alternating bits: namely, if two adjacent bits will always have different values.
Example 1:
Input: 5
Output: True
Explanation:
The binary representation of 5 is: 101
Example 2:
Input: 7
Output: False
Explanation:
The binary representation of 7 is: 111.
Example 3:
Input: 11
Output: False
Explanation:
The binary representation of 11 is: 1011.
Example 4:
Input: 10
Output: True
Explanation:
The binary representation of 10 is: 1010.
https://leetcode.com/problems/binary-number-with-alternating-bits/discuss/108427/Oneliners-(C%2B%2B-Java-Ruby-Python)

Solution 1 - Cancel Bits

bool hasAlternatingBits(int n) {
    return !((n ^= n/4) & n-1);
}
Xor the number with itself shifted right twice and check whether everything after the leading 1-bit became/stayed 0. Xor is 0 iff the bits are equal, so we get 0-bits iff the pair of leading 1-bit and the 0-bit in front of it are repeated until the end.
    000101010
  ^ 000001010
  = 000100000

Solution 2 - Complete Bits

bool hasAlternatingBits(int n) {
    return !((n ^= n/2) & n+1);
}
Xor the number with itself shifted right once and check whether everything after the leading 1-bit became/stayed 1. Xor is 1 iff the bits differ, so we get 1-bits iff starting with the leading 1-bit, the bits alternate between 1 and 0.
    000101010
  ^ 000010101
  = 000111111

Solution 3 - Positive RegEx

public boolean hasAlternatingBits(int n) {
    return Integer.toBinaryString(n).matches("(10)*1?");
}
It's simple to describe with a regular expression.

Solution 4 - Negative RegEx

def has_alternating_bits(n)
  n.to_s(2) !~ /00|11/
end
It's even simpler to describe what we don't want: two zeros or ones in a row.

Solution 5 - Negative String

def hasAlternatingBits(self, n):
    return '00' not in bin(n) and '11' not in bin(n)
Same as before, just not using regex.

Solution 6 - Golfed

def has_alternating_bits(n)
  (n^=n/2)&n+1<1
end

Solution 7 - Recursion

def has_alternating_bits(n)
  n < 3 || n%2 != n/2%2 && has_alternating_bits(n/2)
end
Compare the last two bits and recurse with the last bit shifted out.

Solution 8 - Complete Bits + RegEx

public boolean hasAlternatingBits(int n) {
    return Integer.toBinaryString(n ^ n/2).matches("1+");
}

  • Time Complexity: O(1). For arbitrary inputs, we do O(w) work, where w is the number of bits in n. However, w \leq 32.
  • Space complexity: O(1), or alternatively O(w).
    public boolean hasAlternatingBits(int n) {
        String bits = Integer.toBinaryString(n);
        for (int i = 0; i < bits.length() - 1; i++) {
            if (bits.charAt(i) == bits.charAt(i+1)) {
                return false;
            }
        }
        return true;
    }

https://leetcode.com/problems/binary-number-with-alternating-bits/discuss/113933/Java-super-simple-explanation-with-inline-example
    public boolean hasAlternatingBits(int n) {
        int cur = 0, pre = -1;
        while(n != 0) {
            cur = n & 1;
            if(cur == pre) return false;
            n >>>= 1;
            pre = cur;
        }
        return true;
    }
Approach #2: Divide By Two [Accepted]
We can get the last bit and the rest of the bits via n % 2 and n // 2 operations. Let's remember cur, the last bit of n. If the last bit ever equals the last bit of the remaining, then two adjacent bits have the same value, and the answer is False. Otherwise, the answer is True.
Also note that instead of n % 2 and n // 2, we could have used operators n & 1 and n >>= 1 instead.
Time Complexity: O(1). For arbitrary inputs, we do O(w) work, where w is the number of bits in n. However, w \leq 32.

    public boolean hasAlternatingBits(int n) {
        int cur = n % 2;
        n /= 2;
        while (n > 0) {
            if (cur == n % 2) return false;
            cur = n % 2;
            n /= 2;
        }
        return true;
    }

Labels

LeetCode (1432) GeeksforGeeks (1122) LeetCode - Review (1067) Review (882) Algorithm (668) to-do (609) Classic Algorithm (270) Google Interview (237) Classic Interview (222) Dynamic Programming (220) DP (186) Bit Algorithms (145) POJ (141) Math (137) Tree (132) LeetCode - Phone (129) EPI (122) Cracking Coding Interview (119) DFS (115) Difficult Algorithm (115) Lintcode (115) Different Solutions (110) Smart Algorithm (104) Binary Search (96) BFS (91) HackerRank (90) Binary Tree (86) Hard (79) Two Pointers (78) Stack (76) Company-Facebook (75) BST (72) Graph Algorithm (72) Time Complexity (69) Greedy Algorithm (68) Interval (63) Company - Google (62) Geometry Algorithm (61) Interview Corner (61) LeetCode - Extended (61) Union-Find (60) Trie (58) Advanced Data Structure (56) List (56) Priority Queue (53) Codility (52) ComProGuide (50) LeetCode Hard (50) Matrix (50) Bisection (48) Segment Tree (48) Sliding Window (48) USACO (46) Space Optimization (45) Company-Airbnb (41) Greedy (41) Mathematical Algorithm (41) Tree - Post-Order (41) ACM-ICPC (40) Algorithm Interview (40) Data Structure Design (40) Graph (40) Backtracking (39) Data Structure (39) Jobdu (39) Random (39) Codeforces (38) Knapsack (38) LeetCode - DP (38) Recursive Algorithm (38) String Algorithm (38) TopCoder (38) Sort (37) Introduction to Algorithms (36) Pre-Sort (36) Beauty of Programming (35) Must Known (34) Binary Search Tree (33) Follow Up (33) prismoskills (33) Palindrome (32) Permutation (31) Array (30) Google Code Jam (30) HDU (30) Array O(N) (29) Logic Thinking (29) Monotonic Stack (29) Puzzles (29) Code - Detail (27) Company-Zenefits (27) Microsoft 100 - July (27) Queue (27) Binary Indexed Trees (26) TreeMap (26) to-do-must (26) 1point3acres (25) GeeksQuiz (25) Merge Sort (25) Reverse Thinking (25) hihocoder (25) Company - LinkedIn (24) Hash (24) High Frequency (24) Summary (24) Divide and Conquer (23) Proof (23) Game Theory (22) Topological Sort (22) Lintcode - Review (21) Tree - Modification (21) Algorithm Game (20) CareerCup (20) Company - Twitter (20) DFS + Review (20) DP - Relation (20) Brain Teaser (19) DP - Tree (19) Left and Right Array (19) O(N) (19) Sweep Line (19) UVA (19) DP - Bit Masking (18) LeetCode - Thinking (18) KMP (17) LeetCode - TODO (17) Probabilities (17) Simulation (17) String Search (17) Codercareer (16) Company-Uber (16) Iterator (16) Number (16) O(1) Space (16) Shortest Path (16) itint5 (16) DFS+Cache (15) Dijkstra (15) Euclidean GCD (15) Heap (15) LeetCode - Hard (15) Majority (15) Number Theory (15) Rolling Hash (15) Tree Traversal (15) Brute Force (14) Bucket Sort (14) DP - Knapsack (14) DP - Probability (14) Difficult (14) Fast Power Algorithm (14) Pattern (14) Prefix Sum (14) TreeSet (14) Algorithm Videos (13) Amazon Interview (13) Basic Algorithm (13) Codechef (13) Combination (13) Computational Geometry (13) DP - Digit (13) LCA (13) LeetCode - DFS (13) Linked List (13) Long Increasing Sequence(LIS) (13) Math-Divisible (13) Reservoir Sampling (13) mitbbs (13) Algorithm - How To (12) Company - Microsoft (12) DP - Interval (12) DP - Multiple Relation (12) DP - Relation Optimization (12) LeetCode - Classic (12) Level Order Traversal (12) Prime (12) Pruning (12) Reconstruct Tree (12) Thinking (12) X Sum (12) AOJ (11) Bit Mask (11) Company-Snapchat (11) DP - Space Optimization (11) Dequeue (11) Graph DFS (11) MinMax (11) Miscs (11) Princeton (11) Quick Sort (11) Stack - Tree (11) 尺取法 (11) 挑战程序设计竞赛 (11) Coin Change (10) DFS+Backtracking (10) Facebook Hacker Cup (10) Fast Slow Pointers (10) HackerRank Easy (10) Interval Tree (10) Limited Range (10) Matrix - Traverse (10) Monotone Queue (10) SPOJ (10) Starting Point (10) States (10) Stock (10) Theory (10) Tutorialhorizon (10) Kadane - Extended (9) Mathblog (9) Max-Min Flow (9) Maze (9) Median (9) O(32N) (9) Quick Select (9) Stack Overflow (9) System Design (9) Tree - Conversion (9) Use XOR (9) Book Notes (8) Company-Amazon (8) DFS+BFS (8) DP - States (8) Expression (8) Longest Common Subsequence(LCS) (8) One Pass (8) Quadtrees (8) Traversal Once (8) Trie - Suffix (8) 穷竭搜索 (8) Algorithm Problem List (7) All Sub (7) Catalan Number (7) Cycle (7) DP - Cases (7) Facebook Interview (7) Fibonacci Numbers (7) Flood fill (7) Game Nim (7) Graph BFS (7) HackerRank Difficult (7) Hackerearth (7) Inversion (7) Kadane’s Algorithm (7) Manacher (7) Morris Traversal (7) Multiple Data Structures (7) Normalized Key (7) O(XN) (7) Radix Sort (7) Recursion (7) Sampling (7) Suffix Array (7) Tech-Queries (7) Tree - Serialization (7) Tree DP (7) Trie - Bit (7) 蓝桥杯 (7) Algorithm - Brain Teaser (6) BFS - Priority Queue (6) BFS - Unusual (6) Classic Data Structure Impl (6) DP - 2D (6) DP - Monotone Queue (6) DP - Unusual (6) DP-Space Optimization (6) Dutch Flag (6) How To (6) Interviewstreet (6) Knapsack - MultiplePack (6) Local MinMax (6) MST (6) Minimum Spanning Tree (6) Number - Reach (6) Parentheses (6) Pre-Sum (6) Probability (6) Programming Pearls (6) Rabin-Karp (6) Reverse (6) Scan from right (6) Schedule (6) Stream (6) Subset Sum (6) TSP (6) Xpost (6) n00tc0d3r (6) reddit (6) AI (5) Abbreviation (5) Anagram (5) Art Of Programming-July (5) Assumption (5) Bellman Ford (5) Big Data (5) Code - Solid (5) Code Kata (5) Codility-lessons (5) Coding (5) Company - WMware (5) Convex Hull (5) Crazyforcode (5) DFS - Multiple (5) DFS+DP (5) DP - Multi-Dimension (5) DP-Multiple Relation (5) Eulerian Cycle (5) Graph - Unusual (5) Graph Cycle (5) Hash Strategy (5) Immutability (5) Java (5) LogN (5) Manhattan Distance (5) Matrix Chain Multiplication (5) N Queens (5) Pre-Sort: Index (5) Quick Partition (5) Quora (5) Randomized Algorithms (5) Resources (5) Robot (5) SPFA(Shortest Path Faster Algorithm) (5) Shuffle (5) Sieve of Eratosthenes (5) Strongly Connected Components (5) Subarray Sum (5) Sudoku (5) Suffix Tree (5) Swap (5) Threaded (5) Tree - Creation (5) Warshall Floyd (5) Word Search (5) jiuzhang (5)

Popular Posts