MapTwo.java

/**
 * 
 */
package coding.bat.solutions;

import java.util.HashMap;
import java.util.Map;

/**
 * @author Aman Shekhar
 *
 */
public class MapTwo {

	/**
	 * @param args
	 */
	public static void main(String[] args) {
		// TODO Auto-generated method stub

	}
	
	// Given an array of strings, return a Map<String, Integer> containing a key for
	// every different string in the array, always with the value 0. For example the
	// string "hello" makes the pair "hello":0. We'll do more complicated counting
	// later, but for this problem the value is simply 0.
	//
	//
	// word0(["a", "b", "a", "b"]) → {"a": 0, "b": 0}
	// word0(["a", "b", "a", "c", "b"]) → {"a": 0, "b": 0, "c": 0}
	// word0(["c", "b", "a"]) → {"a": 0, "b": 0, "c": 0}

	public Map<String, Integer> word0(String[] strings) {
		Map<String, Integer> map = new HashMap();
		for (String s : strings) {
			map.put(s, 0);
		}
		return map;
	}

	// --------------------------------------------------------------------------------------------


	// Given an array of strings, return a Map<String, Integer> containing a key for
	// every different string in the array, and the value is that string's length.
	//
	//
	// wordLen(["a", "bb", "a", "bb"]) → {"bb": 2, "a": 1}
	// wordLen(["this", "and", "that", "and"]) → {"that": 4, "and": 3, "this": 4}
	// wordLen(["code", "code", "code", "bug"]) → {"code": 4, "bug": 3}

	public Map<String, Integer> wordLen(String[] strings) {
		Map<String, Integer> map = new HashMap();
		for (String s : strings) {
			map.put(s, s.length());
		}
		return map;
	}

	// --------------------------------------------------------------------------------------------


	// Given an array of non-empty strings, create and return a Map<String, String>
	// as follows: for each string add its first character as a key with its last
	// character as the value.
	//
	//
	// pairs(["code", "bug"]) → {"b": "g", "c": "e"}
	// pairs(["man", "moon", "main"]) → {"m": "n"}
	// pairs(["man", "moon", "good", "night"]) → {"g": "d", "m": "n", "n": "t"}

	public Map<String, String> pairs(String[] strings) {
		Map<String, String> map = new HashMap();
		for (String s : strings) {
			map.put(s.charAt(0) + "", s.charAt(s.length() - 1) + "");
		}
		return map;
	}

	// --------------------------------------------------------------------------------------------


	// The classic word-count algorithm: given an array of strings, return a
	// Map<String, Integer> with a key for each different string, with the value the
	// number of times that string appears in the array.
	//
	//
	// wordCount(["a", "b", "a", "c", "b"]) → {"a": 2, "b": 2, "c": 1}
	// wordCount(["c", "b", "a"]) → {"a": 1, "b": 1, "c": 1}
	// wordCount(["c", "c", "c", "c"]) → {"c": 4}

	public Map<String, Integer> wordCount(String[] strings) {
		Map<String, Integer> map = new HashMap();
		for (String s : strings) {
			String tmp = s;
			if (map.containsKey(tmp)) {
				int count = map.get(tmp);
				map.put(tmp, count + 1);
			} else
				map.put(tmp, 1);
		}
		return map;
	}

	// --------------------------------------------------------------------------------------------


	// Given an array of non-empty strings, return a Map<String, String> with a key
	// for every different first character seen, with the value of all the strings
	// starting with that character appended together in the order they appear in
	// the array.
	//
	//
	// firstChar(["salt", "tea", "soda", "toast"]) → {"s": "saltsoda", "t":
	// "teatoast"}
	// firstChar(["aa", "bb", "cc", "aAA", "cCC", "d"]) → {"a": "aaaAA", "b": "bb",
	// "c": "cccCC", "d": "d"}
	// firstChar([]) → {}
	//
	public Map<String, String> firstChar(String[] strings) {
		Map<String, String> map = new HashMap();
		for (String s : strings) {
			String key = s.charAt(0) + "";
			if (map.containsKey(key)) {
				String value = map.get(key) + s;
				map.put(key, value);
			} else
				map.put(key, s);
		}
		return map;
	}

	// --------------------------------------------------------------------------------------------


	//
	//
	// Loop over the given array of strings to build a result string like this: when
	// a string appears the 2nd, 4th, 6th, etc. time in the array, append the string
	// to the result. Return the empty string if no string appears a 2nd time.
	//
	//
	// wordAppend(["a", "b", "a"]) → "a"
	// wordAppend(["a", "b", "a", "c", "a", "d", "a"]) → "aa"
	// wordAppend(["a", "", "a"]) → "a"

	public String wordAppend(String[] strings) {
		Map<String, Integer> map = new HashMap();
		String string = "";

		for (String s : strings) {
			String key = s;

			if (map.containsKey(key)) {
				int value = map.get(key);
				value++;
				if (value % 2 == 0)
					string += key;
				map.put(key, value);
			} else
				map.put(key, 1);
		}
		return string;
	}

	// --------------------------------------------------------------------------------------------


	// Given an array of strings, return a Map<String, Boolean> where each different
	// string is a key and its value is true if that string appears 2 or more times
	// in the array.
	//
	//
	// wordMultiple(["a", "b", "a", "c", "b"]) → {"a": true, "b": true, "c": false}
	// wordMultiple(["c", "b", "a"]) → {"a": false, "b": false, "c": false}
	// wordMultiple(["c", "c", "c", "c"]) → {"c": true}

	public Map<String, Boolean> wordMultiple(String[] strings) {
		Map<String, Integer> stringCount = new HashMap();
		Map<String, Boolean> map = new HashMap();

		for (String s : strings) {
			String key = s;
			if (stringCount.containsKey(key)) {
				int count = stringCount.get(key);
				count++;
				stringCount.put(key, count);
			} else {
				stringCount.put(key, 1);
			}
			map.put(key, stringCount.get(key) >= 2);
		}
		return map;
	}

	// --------------------------------------------------------------------------------------------


	// We'll say that 2 strings "match" if they are non-empty and their first chars
	// are the same. Loop over and then return the given array of non-empty strings
	// as follows: if a string matches an earlier string in the array, swap the 2
	// strings in the array. When a position in the array has been swapped, it no
	// longer matches anything. Using a map, this can be solved making just one pass
	// over the array. More difficult than it looks.
	//
	//
	// allSwap(["ab", "ac"]) → ["ac", "ab"]
	// allSwap(["ax", "bx", "cx", "cy", "by", "ay", "aaa", "azz"]) → ["ay", "by",
	// "cy", "cx", "bx", "ax", "azz", "aaa"]
	// allSwap(["ax", "bx", "ay", "by", "ai", "aj", "bx", "by"]) → ["ay", "by",
	// "ax", "bx", "aj", "ai", "by", "bx"]

	public String[] allSwap(String[] strings) {
		Map<String, Integer> map = new HashMap();
		for (int i = 0; i < strings.length; i++) {
			if (map.containsKey(strings[i].charAt(0) + "")) {
				String string = strings[i];
				strings[i] = strings[map.get(strings[i].charAt(0) + "")];
				strings[map.get(strings[i].charAt(0) + "")] = string;
				map.remove(strings[i].charAt(0) + "");
			} else
				map.put(strings[i].charAt(0) + "", i);
		}
		return strings;
	}

	// --------------------------------------------------------------------------------------------


	// We'll say that 2 strings "match" if they are non-empty and their first chars
	// are the same. Loop over and then return the given array of non-empty strings
	// as follows: if a string matches an earlier string in the array, swap the 2
	// strings in the array. A particular first char can only cause 1 swap, so once
	// a char has caused a swap, its later swaps are disabled. Using a map, this can
	// be solved making just one pass over the array. More difficult than it looks.
	//
	//
	// firstSwap(["ab", "ac"]) → ["ac", "ab"]
	// firstSwap(["ax", "bx", "cx", "cy", "by", "ay", "aaa", "azz"]) → ["ay", "by",
	// "cy", "cx", "bx", "ax", "aaa", "azz"]
	// firstSwap(["ax", "bx", "ay", "by", "ai", "aj", "bx", "by"]) → ["ay", "by",
	// "ax", "bx", "ai", "aj", "bx", "by"]

	public String[] firstSwap(String[] strings) {
		Map<String, Integer> map = new HashMap();
		for (int i = 0; i < strings.length; i++) {
			String string = String.valueOf(strings[i].substring(0, 1));
			if (map.containsKey(string)) {
				int value = map.get(string);
				if (value == -1)
					continue;
				int pos = map.get(string);
				String temp = strings[pos];
				strings[pos] = strings[i];
				strings[i] = temp;
				map.put(string, -1);
			} else
				map.put(string, i);
		}
		return strings;
	}

}