leetcode刷题数论部分

1.常见面试题型atoi

解题技巧：数据大小：maxint:0x7fffffff 2147483647

                                    minint:0x80000000 -2147483648

数字的转置

class Solution {
public:
    int reverse(int x) {
        //x=1999999999
        long long ans=0;
        const int maxint=0x7fffffff;
        const int minint=0x80000000;
        while(x!=0){
            ans=ans*10+(x%10);
            x/=10;
        }
        if(ansmaxint)
        {ans=0;}
        return ans;
    }
};

字符串转整数

class Solution {
public:
    int myAtoi(string str) {
        const int maxint=0x7fffffff;
        const int minint=0x80000000;
        const long long max=0x100000000;
        long long ans=0;
        bool flag=false;
        int st=0;
        while(st='0')
            {ans=ans*10+str[i]-'0';
              if(ans>maxint) ans=maxint;
            }else
            {break;}
        }
    }
    if( flag ==true ) ans=-ans;
    if(ans>maxint)
        ans=maxint;
    if(ans

4的幂

class Solution {
public:
    bool isPowerOfFour(int num) {
        //2 8 false 2=10 8=1000
        //4 16 false
        //5 101
        if(num<=0) return false;
        return((num&(num-1))==0 &&(num&0x55555555));
    }
};

位1的计算

class Solution {
public:
    int hammingWeight(uint32_t n) {
        int ans=0;
        while(n>=0)
        {
            n=n&(n-1);//置最低位1为0
            ans++;
        }
        return ans;
    }
};

3的幂

class Solution {
public:
    bool isPowerOfThree(int n) {
        //3 9 27 
        //big3%n==0
        //big3=3^k
        //k=log3(maxint)
        if(n<=0) return false;
        const int maxint=0x7fffffff;
        int k=log(maxint)/log(3);
        int big3=pow(3,k);
        return (big3%n==0);
    }
};

各位相加

class Solution {
public:
    int addDigits(int num) {
        if(num==0) return 0;
        return ((num-1)%9+1);
    }
};

Nim Game

class Solution {
public:
    bool canWinNim(int n) {
     return ((n%4)!=0);   
    }
};