优选算法第六讲：模拟

1.替换所有的问号

链接: link

class Solution {
public:
    string modifyString(string s) {
        //遍历字符
        for(int i = 0; i < s.size(); i++)
        {
            if(s[i] == '?')
            {
                for(char ch = 'a'; ch <= 'z'; ch++)
                {
                    if((i == 0 || s[i-1] != ch) && (i == s.size()-1 || s[i+1] != ch))
                    {
                        s[i] = ch;
                        break;
                    }
                }
            }
        }
        return s;
    }
};

2.提莫攻击

链接: link

class Solution {
public:
    int findPoisonedDuration(vector<int>& timeSeries, int duration) {
        int ret = 0;
        for(int left = 0, right = 1; right<timeSeries.size(); left++, right++)
        {
            int cur = timeSeries[right]-timeSeries[left];
            if(cur < duration) ret += cur;
            else ret += duration;
        }
        return ret + duration;
    }
};

3.Z字形变换

链接: link

class Solution {
public:
    string convert(string s, int numRows) {
        if(numRows == 1) return s;
        string ret;
        //先处理第一行
        int d = 2*numRows-2;
        int n = s.size();
        for(int i = 0; i<n; i+=d) ret += s[i];
        //再处理中间的情况
        for(int i = 1; i<numRows-1; i++)
        {
            for(int left = i, right = d-i; left < n || right<n; left+=d, right+=d)
            {
                if(left < n) ret += s[left];
                if(right < n) ret += s[right];
            }
        }
        //最后处理最后一行
        for(int i = numRows-1; i<n; i+=d) ret += s[i];

        return ret;
    }
};

4.外观数列

链接: link

class Solution {
public:
    string countAndSay(int n) {
        string s = "1";
        while(--n)
        {
            string ret;
            for(int left = 0, right = 0; right<s.size(); )
            {
                //right向后寻找第一个不同的元素
                while(right < s.size() && s[left] == s[right]) right++;
                int d = right-left;
                ret += to_string(d) + s[left];
                left = right;
            }
            s = ret;
        }
        return s;
    }
};

5.数青蛙

链接: link

class Solution {
public:
    int minNumberOfFrogs(string croakOfFrogs) {
        string s = "croak";
        int n = s.size();
        vector<int> hash(n);//使用数组替代哈希表

        //创建一个哈希表，用来保存s的下标
        unordered_map<char, int> index;
        for(int i = 0; i<n; i++)
            index[s[i]] = i;

        for(auto e : croakOfFrogs)
        {
            if(e == 'c')
            {
                if(hash[n-1]) hash[n-1]--;
                hash[0]++;
            }
            else
            {
                int i = index[e];
                if(hash[i-1] == 0) return -1;
                hash[i-1]--, hash[i]++;
            }
        }
        for(int i = 0; i<hash.size()-1; i++)
            if(hash[i] != 0)
                return -1;
        return hash[n-1];
    }
};