leetcode 字符串

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class Solution {public:    bool isPalindrome(string s) {        transform(s.begin(), s.end(), s.begin(), ::tolower);        auto first = s.begin(), last = prev(s.end());        while(first < last){            if(!::isalnum(*first)) ++first;            else if(!::isalnum(*last)) --last;            else if(*first != *last) return false;            else {++first, --last;}        }        return true;    }};

解法1:

class Solution {public:    int strStr(string haystack, string needle) {        int m = haystack.length(), n = needle.length();        if(!n) return 0;        for(int i = 0; i < m - n + 1; ++i){            int j = 0;            for(; j < n; ++j)                if(haystack[i + j] != needle[j])                    break;            if(j == n)                return i;        }        return -1;    }};

class Solution {public:    string addBinary(string a, string b) {        string result;        const size_t n = a.size() > b.size() ? a.size() : b.size();        reverse(a.begin(), a.end());        reverse(b.begin(), b.end());        int carry = 0;        for(size_t i = 0; i < n; ++i){            const int ai = i < a.size() ? a[i] - '0' : 0;            const int bi = i < b.size() ? b[i] - '0' : 0;            const int val = (ai + bi + carry) % 2;            carry = (ai + bi + carry) / 2;            result.insert(result.begin(), val + '0');        }        if(carry == 1)            result.insert(result.begin(), '1');        return result;    }};

偷懒，用STL

class Solution {public:    int lengthOfLastWord(string s) {        auto last = find_if(s.rbegin(), s.rend(), ::isalpha);        auto first = find_if_not(last, s.rend(), ::isalpha);        return distance(last, first);    }};

题3.11

class Solution {public:    int map(char c){        switch(c){            case 'I': return 1;            case 'V': return 5;            case 'X': return 10;            case 'L': return 50;            case 'C': return 100;            case 'D': return 500;            case 'M': return 1000;            default: return 0;        }    }    int romanToInt(string s) {        int result = 0;        for(size_t i = 0; i < s.size(); ++i){            if(i > 0 && map(s[i]) > map(s[i - 1]))                result += (map(s[i]) - 2 * map(s[i - 1]));            else                result += map(s[i]);        }        return result;    }};

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