C1-Arrays and String【Cracking the Coding Interview 习题解答】

Cracking the Coding Interview 习题解答 Chapter 1

1.1 Implement an algorithm to determine if a string has all unique characters. What if you can not use additional data structures?

判断字符串是否有重复字符

o(n^2)时间复杂度算法

public boolean hasUnique(String sentence){        for (int i = 0; i < sentence.length(); i++) {            for (int j = 0; j < sentence.length(); j++) {                if(i!=j && sentence.charAt(i)==sentence.charAt(j))                    return false;            }        }        return true;}

o(n)时间复杂度，增加一个Set空间为代价

public boolean hasUnique2(String sentence){        Set<Character> set = new HashSet<Character>();        for (int i = 0; i < sentence.length(); i++) {            if(set.contains(sentence.charAt(i)))                return false;            set.add(sentence.charAt(i));        }        return true;    }

o(n)时间复杂度，假设字符为ASCII码，进一步减少空间损耗

public boolean hasUnique3(String sentence){        boolean[] char_set = new boolean[256];        for (int i = 0; i < sentence.length(); i++) {            int val = sentence.charAt(i);            if(char_set[val]) return false;            char_set[val] = true;        }        return true;}

o(n)时间复杂度，假设字符为'a'~'z'，进一步减少空间，使用一个int，32位足够表示26个字母

public boolean hasUnique4(String sentence){        int checker = 0;        for (int i = 0; i < sentence.length(); i++) {            int val = sentence.charAt(i) - 'a';            if((checker & (1 << val)) > 0) return false;            checker |= (1 << val);        }        return true;}

1.2 Write code to reverse a C-Style String. (C-String means that “abcd” is represented as five characters, including the null character.)

反转字符串

java版本

public char[] reverse(char[] cs){        int i=0, j=cs.length-2;        while(i<j){            char tmp = cs[j];            cs[j--] = cs[i];            cs[i++] = tmp;        }        return cs;}

c++版本

void reverse(char *str) {char * end = str;char tmp;if (str) {while (*end) {++end;}--end;while (str < end) {tmp = *str;*str++ = *end;*end-- = tmp;}}}

1.3 Design an algorithm and write code to remove the duplicate characters in a string without using any additional buffer. NOTE: One or two additional variables are fine. An extra copy of the array is not.
FOLLOW UP
Write the test cases for this method.

1.4 Write a method to decide if two strings are anagrams or not.

1.5 Write a method to replace all spaces in a string with ‘%20’.

1.6 Given an image represented by an NxN matrix, where each pixel in the image is 4 bytes, write a method to rotate the image by 90 degrees. Can you do this in place?

1.7 Write an algorithm such that if an element in an MxN matrix is 0, its entire row and column is set to 0.

1.8 Assume you have a method isSubstring which checks if one word is a substring of another. Given two strings, s1 and s2, write code to check if s2 is a rotation of s1 using only one call to isSubstring (i.e., “waterbottle” is a rotation of “erbottlewat”).