几个经典的小算法

1. 最大子序列和问题

 1 int MaxSubsquenceSum(const int A[],int N){

 2 

 3    int ThisSum,MaxSum,j;

 4 

 5    ThisSum = MaxSum = 0;

 6 

 7    for(j=0;j<N;j++){

 8 

 9       ThisSum += A[j];

10 

11       if(ThisSum > MaxSum)

12 

13           MaxSum = ThisSum;

14 

15       else if(ThisSum < 0)

16 

17           ThisSum = 0;

18 

19    }

20 

21    return MaxSum;

22 

23 }

 

2. 二分查找法

 1 int BinarySearch(const ElementType A[], ElementType X, int N){

 2 

 3    int Low,Mid,High;

 4 

 5    Low=0;High=N-1;

 6 

 7    while(Low <= High){

 8 

 9       Mid = (Low + High)/2;

10 

11       if(a[Mid] < X)

12 

13          Low = Mid + 1;

14 

15       else if(a[Mid] > X)

16 

17          High = Mid -1;

18 

19       else

20 

21          return Mid;

22 

23    }

24 

25    return NotFound;

26 

27 }

 

3.欧几里德算法（求最大公因数）

 1 unsigned int Gcd(unsigned int M,unsigned int N){

 2 

 3    unsigned int Rem;

 4 

 5    while(N > 0){

 6 

 7       Rem = M % N;

 8 

 9       M = N;

10 

11       N = Rem;

12 

13    }

14 

15    return M;

16 

17 }

 

4.幂运算（计算X的n次方）

 1 long int Pow(long int X,unsigned int N){

 2 

 3    if(N == 0) return 1;

 4 

 5    if(N == 1) return X;

 6 

 7    if(IsEven(N)) return Pow(X * X,N/2);

 8 

 9    else return Pow(X * X,N/2) * X;

10 

11 }