LeetCode Week 0

warm up, 希望可以坚持下来

问题集合

1. Hamming Distance （Easy 461）

The Hamming distance between two integers is the number of positions at which the corresponding bits are different.

Given two integers x and y, calculate the Hamming distance.
Note:

0≤x,y<231

Example:

Input: x = 1, y = 4Output: 2Explanation:1   (0 0 0 1)4   (0 1 0 0)       ↑  ↑The above arrows point to positions where the corresponding bits are different.

Solution:

int hammingDistance(int x, int y) {    int diff = x^y;    int distance = 0;    while (diff) {        distance += diff & 1;        diff >>= 1;    }    return distance;}

2.Number Complement (Easy 476)

Given a positive integer, output its complement number. The complement strategy is to flip the bits of its binary representation.
Note:
1. The given integer is guaranteed to fit within the range of a 32-bit signed integer.
2. You could assume no leading zero bit in the integer’s binary representation.
Example 1:

Input: 5Output: 2Explanation: The binary representation of 5 is 101 (no leading zero bits), and its complement is 010. So you need to output 2.

Example 2:

Input: 1Output: 0Explanation: The binary representation of 1 is 1 (no leading zero bits), and its complement is 0. So you need to output 0.

Solution:

int findComplement(int num) {    int helper = -1;    int complement = num ^ helper;    int mask = 0;    while(num > 0) {        mask = (mask << 1) + 1;        num >>= 1;    }    return complement & mask;}

3.Keyboard Row （Easy 500）

Given a List of words, return the words that can be typed using letters of alphabet on only one row’s of American keyboard like the image below.

Note:
1. You may use one character in the keyboard more than once.
2. You may assume the input string will only contain letters of alphabet.

Example 1:

Input: ["Hello", "Alaska", "Dad", "Peace"]Output: ["Alaska", "Dad"]

Solution:

/** * Return an array of size *returnSize. * Note: The returned array must be malloced, assume caller calls free(). */char** findWords(char** words, int wordsSize, int* returnSize) {    *returnSize = 0;    char** result = NULL;    if (wordsSize <= 0) return result;    int rowMap[26] = {1, 2, 2, 1, 0, 1, 1, 1, 0, 1, 1, 1, 2, 2, 0, 0, 0, 0, 1, 0, 0, 2, 0, 2, 0, 2};    int* saveFlags = (int *)malloc(sizeof(int) * wordsSize);    int cellSize = 0;    for (int i = 0; i < wordsSize; i++) {        int lastRow = -1;        int save = 1;        int len = strlen(words[i]);        for (int j = 0; j < len; j++) {            int row = rowMap[(words[i][j] < 'a' ? (words[i][j] + 32) : words[i][j]) - 'a'];            if (lastRow != -1 && row != lastRow) {                save = 0;                break;            }            lastRow = row;        }        saveFlags[i] = save;        if (save) {            (*returnSize)++;            if (cellSize < len) {                cellSize = len;            }        }    }    if ((*returnSize) > 0) {        // alloc memory        result = (char **)malloc(sizeof(char*) * (*returnSize));        for (int i = 0; i < (*returnSize); i++) {            result[i] = (char *)malloc(sizeof(char) * (cellSize + 1));        }        // copy words        int index = 0;        for (int i = 0; i < wordsSize; i++) {            if (saveFlags[i]) {                strcpy(result[index++], words[i]);            }        }    }    return result;