计算数组中连续元素和的最大值

 1 /************************************************************************/
 2 /* 计算数组中连续元素和的最大值所在的区间 
 3 /************************************************************************/
 4 #include "stdio.h"
 5 #include "time.h"
 6 #include "stdlib.h"
 7 
 8 #define PRINT         0       /* 是否打印数组 */
 9 #define SRAND         1       /* 是否打开随机数发生器 */
10 #define ARRAY_MAX_LEN 210000   /* 数组大小 */
11 #define ALG_1         0
12 #define ALG_2         1
13 
14 /* 打印数组元素 */
15 #define PRINTARRAY() \
16 {\
17     for (idx=0; idx < ARRAY_MAX_LEN; idx++)\
18     {\
19         printf("%d ", x[idx]);\
20     }\
21 }
22 
23 #define MAX(a,b)  ((a > b) ? a : b)
24 
25 void main()
26 {
27     /* 随机生成一批数字 */
28     int x[ARRAY_MAX_LEN];
29     int idx=0;
30 
31 #if SRAND
32     srand((unsigned)time(NULL));
33 #endif
34 
35     printf("generating %d rand numbers...\n", ARRAY_MAX_LEN);
36     for (idx=0; idx < ARRAY_MAX_LEN; idx++)
37     {
38         if (idx % 2 == 0)
39         {
40             x[idx] = rand() % 3;
41         }
42         else
43         {
44             x[idx] = -rand() % 8;
45         }
46     }
47     printf("generating done!\n");
48 
49     /* 打印数组元素 */
50 #if PRINT
51     PRINTARRAY();
52 #endif
53 
54     /* 计时开始 */
55     clock_t start, finish;
56     double   duration;
57     start = clock();
58 
59     int maxsofar = 0;    
60     int sum = 0;
61 
62     printf("computing range-sum-max...\n");
63 #if ALG_1
64     /* 计算过程 (1) */
65     for (int i = 0; i < ARRAY_MAX_LEN; i++)
66     {
67         for (int j = i; j < ARRAY_MAX_LEN; j++)
68         {
69             sum += x[j];
70             maxsofar = MAX(maxsofar, sum);
71         }
72         sum = 0;
73     }
74 #endif
75     /* 计算过程 (2) */
76 #if ALG_2
77     int maxendinghere = 0;
78     for (int i = 0; i < ARRAY_MAX_LEN; i++)
79     {
80         maxendinghere = MAX(maxendinghere + x[i], 0);
81         maxsofar = MAX(maxendinghere, maxsofar);
82     }
83 #endif
84     /* 计时结束 */
85     finish = clock();
86     duration = (double)(finish - start) / CLOCKS_PER_SEC;
87 
88     /* 统计输出 */
89     printf("duration: %f seconds\n",duration);
90     printf("range-sum-max: %d\n", maxsofar);
91     getchar();
92 }