Created
November 9, 2017 07:07
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Sentence reverse - need to read the problem carefully, reverse twice and the word goes back to original order.
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using System; | |
class Solution | |
{ | |
public static char[] ReverseWords(char[] arr) // "a b cd" | |
{ | |
if(arr == null || arr.Length == 0) // false | |
{ | |
return new char[0]; | |
} | |
var length = arr.Length; // 6 | |
reverseWordInplace(arr, 0 , length - 1); // "dc b a" | |
// reverse each word | |
int start = 0; | |
for(int index = 0; index < length; index ++) //"dc b a" | |
{ | |
var visit = arr[index]; | |
var isNonSpacer = visit != ' '; // true | |
var isFirst = isNonSpacer && (index == 0 || arr[index - 1] == ' '); // d, false | |
if(isFirst) // true | |
{ | |
start = index; // 0 | |
} | |
var isLast = isNonSpacer && (index == (length - 1) || arr[index + 1] == ' '); // false, true | |
if(isLast) | |
{ | |
reverseWordInplace(arr, start, index); //0, 1 | |
} | |
} | |
return arr; | |
} | |
private static void reverseWordInplace(char[] arr, int start, int end )// "a b cd" 0, 5 -> "dc b a" | |
{ | |
while(start < end) // | |
{ | |
var temp = arr[start]; | |
arr[start] = arr[end]; | |
arr[end] = temp; | |
start ++; // 0 -> 1 | |
end --; // 5 -> 4 | |
} | |
} | |
static void Main(string[] args) | |
{ | |
} | |
} | |
// "a b cd" -> "cd b a" -> each word -> reverse each word -> "cd" | |
// inplace all the time -> reverse the string | |
// last word -> first word, every word the word is reversed, reverse again | |
// instead of API - > by myself | |
// time complexity -> empty char ' ' delimiter | |
// space complexity - O(1) |
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Leetcode 151 - reverse words in a string, medium level algorithm. Need to go over leetcode discussion and figure out what to learn. Nov. 9, 2017