http://acm.hdu.edu.cn/showproblem.php?pid=1024 最大m字段和,题目就不多说了,经典dp
这题坑爹。。。首先不说明m的范围(n<=1000000),还以为有O(n)的算法,吓得不敢做。其次,按照题目给的范围完全可能超int,但是数据事实上int远远够了,害得我__int64读比读int慢两倍,直接TLE。就是因为TLE的原因,害得我数组初始化没有考虑全(其实应该怪自己没有考虑清楚->_->),但事实上,完全可以每次memset一遍,因为超时,不敢==。各种原因,几分钟敲完的水题调了1个多小时!我也是醉了。。。
![](https://images.cnblogs.com/OutliningIndicators/ContractedBlock.gif)
1 #include <iostream> 2 #include <cstdio> 3 #include <cstring> 4 #include <cmath> 5 #include <algorithm> 6 #include <map> 7 #include <stack> 8 #include <string> 9 #include <ctime> 10 #include <queue> 11 #define mem0(a) memset(a, 0, sizeof(a)) 12 #define mem(a, b) memset(a, b, sizeof(a)) 13 #define lson l, m, rt << 1 14 #define rson m + 1, r, rt << 1 | 1 15 #define eps 0.0000001 16 #define lowbit(x) ((x) & -(x)) 17 #define memc(a, b) memcpy(a, b, sizeof(b)) 18 #define x_x(a) ((a) * (a)) 19 #define LL __int64 20 #define DB double 21 #define pi 3.14159265359 22 #define MD 10000007 23 #define INF (int)1e9 24 #define max(a, b) ((a) > (b)? (a) : (b)) 25 using namespace std; 26 int f[1000010][2][2]; 27 int a[1000010]; 28 int main() 29 { 30 //freopen("input.txt", "r", stdin); 31 //freopen("output.txt", "w", stdout); 32 int n, m; 33 while(~scanf("%d%d", &m, &n)) { 34 for(int i = 1; i <= n; i++) { 35 scanf("%d", a + i); 36 } 37 for(int i = 0; i <= n; i++) { 38 f[i][0][0] = 0; 39 f[i][0][1] = -INF; 40 } 41 int now = 1; 42 for(int j = 1; j <= m; j++) { 43 f[0][now][0] = f[0][now][1] = - INF; 44 for(int i = 1; i <= n; i++) { 45 if(i < j) { 46 f[i][now][1] = f[i][now][0]= -INF; 47 continue; 48 } 49 f[i][now][1] = max(max(f[i - 1][now ^ 1][0], f[i - 1][now ^ 1][1]), f[i - 1][now][1]) + a[i]; 50 f[i][now][0] = max(f[i - 1][now][0], f[i - 1][now][1]); 51 } 52 now ^= 1; 53 } 54 printf("%d ", max(f[n][now ^ 1][0], f[n][now ^ 1][1])); 55 } 56 return 0; 57 }