Create reverseWordsInSentenseInConstantMemory

Author: nkatre

reverseWordsInSentenseInConstantMemory

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+
+/*
+ * Question: Inplace reverse a sentence 
+
+You given a sentence of english words and spaces between them. 
+Nothing crazy: 
+1) no double spaces 
+2) no empty words 
+3) no spaces at the ends of a sentence
+
+
+void inplace_reverse(char* arr, int length) {
+    // your solution
+}
+Example: 
+input "I wish you a merry Christmas" 
+output "Christmas merry a you wish I" 
+
+Constrains: O(1) additional memory
+
+
+
+Source: http://www.careercup.com/question?id=5717567253512192
+
+Algorithm: 1. Reverse the words in the sentence
+		   2. Reverse the sentence
+		   
+Example: 
+Input: I wish you a merry Christmas
+step 1 . I hisw uoy a yrrem samtsirhC 
+step 2 . Christmas merry a you wish I
+
+*/
+
+
+
+package reverseWordsInSentenseInConstantMemory;
+
+import java.util.Scanner;
+
+public class UsingReverseWordsFunction {
+public static void main(String[] args) {
+	Scanner in = new Scanner(System.in);
+	try{
+		System.out.println("Enter the sentence whose words needs to be reversed");
+		char[] s = in.nextLine().toCharArray();
+		s=reverseSentence(s);
+		System.out.println(String.valueOf(s));
+		
+	}finally{
+		in.close();
+	}
+}
+/*  Preconditions of the input string given in the question:
+1) no double spaces 
+2) no empty words 
+3) no spaces at the ends of a sentence
+*/
+public static void reverseWord(char[] s,int start, int end){
+	for(;start<end;start++,end--){
+		// Swap start and end characters In Place
+	    s[start] = (char)(s[start]^s[end]);
+	    s[end] = (char)(s[start]^s[end]);
+	    s[start] = (char)(s[start]^s[end]);
+	}
+}
+public static char[] reverseSentence(char[] s){
+	int start = 0;
+	int end = 0;
+	for(int i=0;i<s.length;i++){
+
+		if(s[i]==' '){  // either when we get empty space
+			end=i-1;
+			reverseWord(s, start, end);
+			start=i+1;
+		}
+		if(i==(s.length-1)){  // If we reach the end of the string
+			end=i;
+			reverseWord(s, start, end);
+		}
+	}
+	reverseWord(s, 0, s.length-1);
+	return s;
+	}
+}
+/*
+ * Analysis:
+ *       Time Complexity = O(n) where n = length of the string
+ *       Space Complexity = O(1)
+ */