力扣 模拟专题

263. 丑数

https://leetcode-cn.com/problems/ugly-number/

class Solution {
public:
    bool isUgly(int n) {
        int f4=0;
        if(n==1) return true;
        if(n==0) return false;
        while(n!=1){
            int f1=0,f2=0,f3=0;
            if(n%2==0){
                n/=2;
                f1=1;
                continue;
            }
            else if(n%3==0){
                n/=3;
                f2=1;
                continue;
            }
            else if(n%5==0){
                n/=5;
                f3=1;
                continue;
            }
            if(!f1 && !f2 && !f3){
                f4=1;
                break;
            }
        }
        if(f4) return false;
        else return true;
    }
};

67. 二进制求和

https://leetcode-cn.com/problems/add-binary/

class Solution {
public:
    string addBinary(string a, string b) {
        reverse(a.begin(),a.end());
        reverse(b.begin(),b.end());
        int t=0;
        string c;
        for(int i=0;i<a.size() || i<b.size();i++){
            int va=i>=a.size() ?0:a[i]-'0'; //如果a已经用完了就默认0 
            int vb=i>=b.size() ?0:b[i]-'0';
            int temp=va+vb+t;
            t=temp/2;
            temp%=2;
            c+=to_string(temp);
        }
        if(t)//有进位
            c+='1';
        reverse(c.begin(),c.end());
        return c;
    }
};

504. 七进制数

https://leetcode-cn.com/problems/base-7/

class Solution {
public:
    string convertToBase7(int num) {
        bool isFu=false;
        if(num<0){
            isFu=true;
            num*=-1;
        }
        if(!num) return "0";
        string res;
        while(num){
            res+=to_string(num%7);
            num/=7;
        }
        if(isFu) res+="-";
        reverse(res.begin(),res.end());
        return res;
    }
};

54. 螺旋矩阵

https://leetcode-cn.com/problems/spiral-matrix/

class Solution {
public:
    int vis[105][105]={0};
    int dx[4]={0,1,0,-1},dy[4]={1,0,-1,0};
    vector<int> spiralOrder(vector<vector<int>>& matrix) {
        vector<int>ans;
        vis[0][0]=1;
        ans.push_back(matrix[0][0]);
        int n=matrix.size(),m=matrix[0].size();
        int temp=1,N=n*m;
        int dir=0;
        int ox=0,oy=0;
        while(temp<N){
            int nx=ox+dx[dir],ny=oy+dy[dir];
            if(nx>=0 && nx<n && ny>=0 && ny<m && !vis[nx][ny]){
                vis[nx][ny]=1;
                ans.push_back(matrix[nx][ny]);
                ox=nx;
                oy=ny;
                temp++;
            }
            else {
                dir+=1;
                dir%=4;
            }

        }
        return ans;
    }
};

24. 两两交换链表中的节点

https://leetcode-cn.com/problems/swap-nodes-in-pairs/
链表题主要靠画图

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode() : val(0), next(nullptr) {}
 *     ListNode(int x) : val(x), next(nullptr) {}
 *     ListNode(int x, ListNode *next) : val(x), next(next) {}
 * };
 */
class Solution {
public:
    ListNode* swapPairs(ListNode* head) {
        auto dummy=new ListNode();
        dummy->next=head;
        auto p=dummy;
        while(p && p->next && p->next->next){
            auto a=p->next;
            auto b=p->next->next;
            p->next=b;
            a->next=b->next;
            b->next=a;
            p=a;
        }
        return dummy->next;
    }
};

481. 神奇字符串

https://leetcode-cn.com/problems/magical-string/

class Solution {
public:
    int magicalString(int n) {
         string s="122";
        for(int i=2,k=1;i<n;i++,k=3-k){
            for(int j=0;j<s[i]-'0';j++){
                s+=to_string(k);
            }
        }
        int res=0;
        for(int i=0;i<n;i++){
            res+=s[i]=='1';
        }
        return res;

    }
};

71. 简化路径(字符串模拟)

https://leetcode-cn.com/problems/simplify-path/

class Solution {
public:
    string simplifyPath(string path) {
        path+='/';//处理边界情况
        string res,s;
        for(auto c:path){
            if(res.empty()) res+=c;
            else if(c!='/'){
                s+=c;
               // cout<<s<<endl;
            } 
            else {
                    if(s==".."){
                        if(res.size()>1){//存在上一级目录
                            res.pop_back();//删除尾巴的'/'
                            while(res.back()!='/') res.pop_back();//一直删除到开头的'/'
                        }
                    }
                    else if(s!="." && s!=""){
                            //不属于上面两种情况就加入
                            res+=s;
                            res+='/';
                        }
                    s="";//清空
                }
        }
        if(res.size()>1) res.pop_back();
        return res;
    }
};

12. 整数转罗马数字

class Solution {
public:
    string intToRoman(int num) {
        int values[]={1000,900,500,400,100,90,50,40,10,9,5,4,1};
        string reps[]={"M","CM","D","CD","C","XC","L","XL","X","IX","V","IV","I"};
        string res;
        for(int i=0;i<13;i++){
            while(num>=values[i]){
                num-=values[i];
                res+=reps[i];
            }
        }
        return res;
    }
};