计算最大子段（分治法）

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这个程序使用分治法计算最大子段，结果为最大子段之和，用递归程序实现。

原始数据使用随机函数生成。

采用结构化程序设计，可以很容易改为从标准输入或文件读入数据，只需要修改函数getData即可。

数据个数由宏定义给出，也可以轻松地改为输入。

/* * 最大子段算法程序 */#include <stdio.h>#include <stdlib.h>#include <time.h>#define N 13void getData(int [], int);int maxsumfun(int a[], int left, int right);int main(void){    int a[N], i;    getData(a, N); /* 获得数据放入数组a中 */    printf("datas: ");    for (i = 0; i < N; i++)        printf("%d ", a[i]);    printf("\n");    int ms;    ms = maxsumfun(a, 0, N - 1);    printf("maxsum=%d\n", ms);    return 0;}int maxsumfun(int a[], int left, int right){    int maxsum = 0;    if(left == right)    {        if(a[left] > 0)            maxsum = a[left];        else            maxsum = 0;    }    else    {        int mid, leftsum, rightsum, midsum;        mid = (left + right) / 2;        leftsum = maxsumfun(a, left, mid);        rightsum = maxsumfun(a, mid+1, right);        int leftsum1 = 0;        int lefts = 0;        int i;        for(i=mid; i>=left; i--)        {            lefts += a[i];            if(lefts > leftsum1)                leftsum1 = lefts;        }        int rightsum1 = 0;        int rights = 0;        for(i=mid+1; i<=right; i++)        {            rights += a[i];            if(rights > rightsum1)                rightsum1 = rights;        }        midsum = leftsum1 + rightsum1;        if(midsum < leftsum)            maxsum = leftsum;        else            maxsum = midsum;        if(maxsum < rightsum)            maxsum = rightsum;    }    return maxsum;}void getData(int d[], int n){    time_t t;    srand((unsigned) time(&t));  /* 设置随机数起始值 */    int i;    for(i=0; i < n; i++)        d[i] = rand() % 30 - 10; /* 获得-10--20之间的整数值 */}

关键代码：

// 递归计算最大子段int maxsumfun(int a[], int left, int right){    int maxsum = 0;    if(left == right)    {        if(a[left] > 0)            maxsum = a[left];        else            maxsum = 0;    }    else    {        int mid, leftsum, rightsum, midsum;        mid = (left + right) / 2;        leftsum = maxsumfun(a, left, mid);        rightsum = maxsumfun(a, mid+1, right);        int leftsum1 = 0;        int lefts = 0;        int i;        for(i=mid; i>=left; i--)        {            lefts += a[i];            if(lefts > leftsum1)                leftsum1 = lefts;        }        int rightsum1 = 0;        int rights = 0;        for(i=mid+1; i<=right; i++)        {            rights += a[i];            if(rights > rightsum1)                rightsum1 = rights;        }        midsum = leftsum1 + rightsum1;        if(midsum < leftsum)            maxsum = leftsum;        else            maxsum = midsum;        if(maxsum < rightsum)            maxsum = rightsum;    }    return maxsum;}

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