Palindrome problem

Problem

The palindrome problem is another classic algorithm question.
Given the sentence, write the code checking if the sentence is a palindrome. Any non-alphabet characters should be ignored.

Examples:

A car, a man, a maraca.
A dog, a plan, a canal: pagoda.
A dog! A panic in a pagoda!
A lad named E. Mandala
A man, a plan, a canal: Panama.

Answer

The algorithm should ignore all but the alphabet. The expected running time is O(N).
This algorithm is quite straightforward.

We can set two pointers: start, and end. start pointer begins with the 0th position and the end pointer starts with $N-1$th position.

Each time we compare the characters pointed by these two points. If they don't match, it is not a palindrome.

If they do, increment a start pointer by 1 and decrement an end pointer by 1 and perform the comparison.

Repeat this process until start >= end.

If you have questions, feel free to add them to the comments.

Here is the code
end of the code

UPDATE(2019-07-31): Solved the problem again. Had a bug in the logic.



Practice statistics

7:15: to write up the code
2:10: to debug the code. (1 bug in the while loop)

UPDATE(2022-06-22): Solve the problem again.


06:42: for algorithm and pseudo code
07:08: coding
03:30: code review

Comments

Post a Comment

Popular posts from this blog

Planting flowers with no adjacent flower plots

Image
Problem Suppose you have a long flowerbed in which some of the plots are planted and some are not. However, flowers cannot be planted in adjacent plots - they would compete for water and both would die. Given a flowerbed (represented as an array containing booleans), return if a given number of new flowers can be planted in it without violating the no-adjacent-flowers rule  Sample inputs  Input: 1,0,0,0,0,0,1,0,0  3 => true  4 => false  Input: 1,0,0,1,0,0,1,0,0  1 => true  2 => false  input: 0  1 => true  2 => false  public boolean canPlaceFlowers(List flowerbed, int numberToPlace) {  // Implementation here  }
Read more
  Given an array of  intervals  where  intervals[i] = [start i , end i ] , merge all overlapping intervals, and return  an array of the non-overlapping intervals that cover all the intervals in the input . Example 1: Input: intervals = [[1,3],[2,6],[8,10],[15,18]] Output: [[1,6],[8,10],[15,18]] Explanation: Since intervals [1,3] and [2,6] overlap, merge them into [1,6]. Example 2: Input: intervals = [[1,4],[4,5]] Output: [[1,5]] Explanation: Intervals [1,4] and [4,5] are considered overlapping.   Constraints: 1 <= intervals.length <= 10 4 intervals[i].length == 2 0 <= start i <= end i <= 10 4
Read more

Find the maximum number of bomb that can be detonated

  Problem You are given a list of bombs. The range of a bomb is defined as the area where its effect can be felt. This area is in the shape of a circle with the center as the location of the bomb. The bombs are represented by a 0-indexed 2D integer array bombs where bombs[i] = [xi, yi, ri]. xi and yi denote the X-coordinate and Y-coordinate of the location of the ith bomb, whereas ri denotes the radius of its range. You may choose to detonate a single bomb. When a bomb is detonated, it will detonate all bombs that lie in its range.  These bombs will further detonate the bombs that lie in their ranges. Given the list of bombs, return the maximum number of bombs that can be detonated if you are allowed to detonate only one bomb. Input: bombs = [[2,1,3],[6,1,4]] Output: 2 Explanation: The above figure shows the positions and ranges of the 2 bombs. If we detonate the left bomb, the right bomb will not be affected. But if we detonate the right bomb, both bombs will be detonated. So...
Read more