LeetCode 2016 345,342,38,257,303,278

最新推荐文章于 2023-03-20 11:17:12 发布

原创最新推荐文章于 2023-03-20 11:17:12 发布 · 491 阅读

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345 Reverse Vowels of a String

class Solution {
public:
    string reverseVowels(string s)
    {
        int len=s.length();
        if (len==0) return "";
        int flag[300]={0};
        flag['a']=1;flag['e']=1;
        flag['i']=1;flag['o']=1;
        flag['u']=1;
        flag['A']=1;flag['E']=1;
        flag['I']=1;flag['O']=1;
        flag['U']=1;
        string vow="";
        int j=-1;
        for(int i=0;i<len;i++)
            if (flag[s[i]]==1) vow=s[i]+vow;
        for(int i=0;i<len;i++)
            if (flag[s[i]]==1)
            {
                j++;
                s[i]=vow[j];
            }
        return s;
    }
};

342 Power of Four

class Solution {
public:
    bool isPowerOfFour(int num)
    {
        if(num==0) return false;
        int x=floor(sqrt(num));
        if (x*x!=num) return false;
        if ((x & (x-1)) == 0)
            return true;
        else return false;
    }
};

38 Count and Say

class Solution {
public:
    string countAndSay(int n)
    {
        if (n==0) return 0;
        if (n==1) return "1";
        string last="1";
        string cur="";
        for(int i=2;i<=n;i++)
        {
            char pre='*';
            int cnt;
            last+='#';
            int len=last.length();
            for(int j=0;j<len;j++)
            {
                if (last[j]==pre)
                    cnt++;
                else
                {
                    if (j!=0)
                        cur+=toString(cnt)+pre;
                    cnt=1;
                }
                pre=last[j];
            }
            last=cur;
            cur="";
        }
        return last;
    }
    string toString(int x)
    {
        string ans="";
        char ch[10]={'0','1','2','3','4','5','6','7','8','9'};
        while (x!=0)
        {
            ans=ch[x%10]+ans;
            x=x/10;
        }
        return ans;
    }
};

257 Binary Tree Paths

WA：
1.漏掉了只有根节点的情况，比如1，结果应为“1”
2.数转换成string的函数toString，一开始忘了考虑负数的情况，原来也是会有的。

class Solution {
public:
    vector<string> ans;
    vector<string> binaryTreePaths(TreeNode* root)
    {
        ans.clear();
        if (root==NULL) return ans;
        if (root->left==NULL && root->right==NULL)
            ans.push_back(toString(root->val));
        else
        {
            if (root->left!=NULL)
                findAllPaths(root->left,toString(root->val));
            if (root->right!=NULL)
                findAllPaths(root->right,toString(root->val));
        }
        return ans;
    }
    void findAllPaths(TreeNode* root,string paths)
    {
        paths+="->"+toString(root->val);
        if (root->left==NULL && root->right==NULL)
        {
            ans.push_back(paths);
            return ;
        }
        if (root->left!=NULL) findAllPaths(root->left,paths);
        if (root->right!=NULL) findAllPaths(root->right,paths);
        return ;
    }
    string toString(int x)
    {
        string ans="";
        if (x==0) return "0";
        bool flag=false;
        if (x<0)
        {
            flag=true;
            x=-x;
        }
        char ch[10]={'0','1','2','3','4','5','6','7','8','9'};
        while (x!=0)
        {
            ans=ch[x%10]+ans;
            x=x/10;
        }
        if (flag) ans="-"+ans;
        return ans;
    }
};

303 Range Sum Query - Immutable

class NumArray {
public:
    vector<int> preSum;
    NumArray(vector<int> &nums)
    {
        preSum.clear();
        int len=nums.size();
        preSum.resize(len+5);
        preSum[0]=0;
        for(int i=0;i<len;i++)
        {
            preSum[i+1]=preSum[i]+nums[i];
        }
        preSum[len+1]=preSum[len];
    }

    int sumRange(int i, int j)
    {
        return preSum[j+1]-preSum[i];
    }
};

278 First Bad Version

TLE原因：
	mid直接用了(left+right)/2,所以TLE了。
	应该改成 mid = left+(right-left)/2；

看了一个讨论的题解
	1. 用一个ans变量来存返回结果，如果mid是true的话，ans=mid，此时right=mid-1而不是mid
	2. while的条件是left<=right，因为left和right的更新是mid+1和mid-1，这样条件就不是left<right
	3. 官网题解用的是我TLE的方式，不过返回了left而非right

看了讨论的题解改的：
// Forward declaration of isBadVersion API.
bool isBadVersion(int version);

class Solution {
public:
    int firstBadVersion(int n)
    {
        int left=1,right=n;
        int mid;
        int ans=-1;
        while (left<=right)
        {
            mid=left+(right-left)/2;
            if (isBadVersion(mid))
            {
                ans=mid;
                right=mid-1;
            }
            else
            {
                left=mid+1;
            }
        }
        return ans;
    }
  
};

看了官网题解，发现了TLE的问题改的：
// Forward declaration of isBadVersion API.
bool isBadVersion(int version);

class Solution {
public:
    int firstBadVersion(int n)
    {
        int left=1,right=n;
        int mid;
        while (left<right)
        {
            mid=(left+right)/2;
            if (isBadVersion(mid))
            {
                right=mid;
            }
            else
            {
                left=mid+1;
            }
        }
        return left;
    }
  
};