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_318.java
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_318.java
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package com.fishercoder.solutions;
public class _318 {
public static class Solution1 {
//Inspired by this awesome post: https://discuss.leetcode.com/topic/35539/java-easy-version-to-understand
//Idea: this question states that all words consisted of lower case (total only 26 unique chars),
//this is a big hint that we could use integer (total 32 bits) to represent each char
//values[i] means how many unique characters this string words[i] has
public int maxProduct(String[] words) {
if (words == null || words.length == 0) {
return 0;
}
int len = words.length;
int[] values = new int[len];
for (int i = 0; i < words.length; i++) {
String word = words[i];
for (int j = 0; j < words[i].length(); j++) {
values[i] |= 1 << (word.charAt(j)
- 'a');//the reason for left shift by this number "word.charAt(j) -'a'" is for 'a', otherwise 'a' - 'a' will be zero and 'a' will be missed out.
}
}
int maxProduct = 0;
for (int i = 0; i < words.length; i++) {
for (int j = 0; j < words.length; j++) {
//check if values[i] AND values[j] equals to zero, this means they share NO common chars
if ((values[i] & values[j]) == 0
&& words[i].length() * words[j].length() > maxProduct) {
maxProduct = words[i].length() * words[j].length();
}
}
}
return maxProduct;
}
}
public static void main(String... strings) {
_318 test = new _318();
String[] words = new String[]{"abcw", "baz", "foo", "bar", "xtfn", "abcdef"};
//The following is to understand what does left shift by 1 mean:
//the tricky part is to understand how it's written for me:
// "x << y" means left shift x by y bits
//left shift is equivalent to multiplication of powers of 2, so "4 << 1" equals to " 4 * 2^1"
//similarly, "4 << 3" equals to "4 * 2^3" which equals "4 * 8"
String sample = "f";
int bits = 0;
int shiftLeftByHowMany = 0;
int shiftLeftResult = 0;
for (int j = 0; j < sample.length(); j++) {
shiftLeftByHowMany = sample.charAt(j) - 'a';
shiftLeftResult = 1 << shiftLeftByHowMany;
bits |= 1 << (sample.charAt(j) - 'a');
//this means shift left 1 by "sample.charAt(j) -'a'" bits
System.out.println("nonShiftLeft = " + shiftLeftByHowMany + "\tnonShiftLeft binary form is: " + Integer.toBinaryString(shiftLeftByHowMany)
+ "\nshiftLeft = " + shiftLeftResult + "\tshiftLeft binary form is: " + Integer.toBinaryString(shiftLeftResult)
+ "\nbits = " + bits + "\tbits binary form is: " + Integer.toBinaryString(bits));
System.out.println(shiftLeftResult == (1 * Math.pow(2, shiftLeftByHowMany)));
}
//similarly, right shift is written like this: "x >> y", means shift x by y bits
//4 >> 3 equals 4 * 2^3, see below:
System.out.println(4 * 8 == (4 * Math.pow(2, 3)));
}
}