HDU1003

    xiaoxiao2021-03-25  87

    Max Sum

    *Time Limit: 2000/1000 MS (Java/Others) Memory Limit: 65536/32768 K (Java/Others) Total Submission(s): 236675 Accepted Submission(s): 55857*

    Problem Description Given a sequence a[1],a[2],a[3]……a[n], your job is to calculate the max sum of a sub-sequence. For example, given (6,-1,5,4,-7), the max sum in this sequence is 6 + (-1) + 5 + 4 = 14.

    Input The first line of the input contains an integer T(1<=T<=20) which means the number of test cases. Then T lines follow, each line starts with a number N(1<=N<=100000), then N integers followed(all the integers are between -1000 and 1000).

    Output For each test case, you should output two lines. The first line is “Case #:”, # means the number of the test case. The second line contains three integers, the Max Sum in the sequence, the start position of the sub-sequence, the end position of the sub-sequence. If there are more than one result, output the first one. Output a blank line between two cases.

    Sample Input

    2 5 6 -1 5 4 -7 7 0 6 -1 1 -6 7 -5

    Sample Output

    Case 1: 14 1 4

    Case 2: 7 1 6


    这道题是用动态规划求得最大和子序列,子序列指的是连续的一组数列,不是断断续续的数列。

    array[i]的值表示 以第i个数字为结尾的子序列的最大和

    array[1]; array[2] = max{array[1]+array[2], array[1]}; array[3] = max{array[1]+array[2]+array[3], array[2]+array[3], array[3]}; array[4] = max{array[1]+array[2]+array[3]+array[4], array[2]+array[3]+array[4], array[3]+array[4], array[4]}; ……

    最后的最大和的值就是这里面的最大值。

    简化一下,用一个变量maxSum来记录array计算运行当中的最大值,sum表示连续子序列的和,x和y表示起始点和终止点。 如果sum > maxSum,则maxSum=sum,并更新x和y的值; 如果sum < maxSum,表示当前的array值是负值,但是之后的数字可能会让sum值再次大于maxSum的值(相等同理); 如果sum<0,则舍弃这一段子序列,因为这一段子序列只会使整个序列的和减小,更新temp标志。 (注意 只有当sum>maxSum时才能更新x和y的值,也就是说temp标记更改之后可能并没有出现比maxSum还大的值)


    #include <cstdio> using namespace std; #define MaxSize 100005 int arr[MaxSize]; int main() { int T; scanf("%d",&T); int cnt; for(cnt=1; cnt<=T; cnt++) { int N,i; scanf("%d",&N); for(i=1; i<=N; i++) { scanf("%d",&arr[i]); } int maxSum=-100000,sum=0,x=1,y=1,temp=1; for(i=1; i<=N; i++) { sum += arr[i]; if(sum > maxSum) { maxSum = sum; x=temp; y=i; } if(sum < 0) { sum = 0; temp=1+i; } } printf("Case %d:\n",cnt); printf("%d %d %d\n",maxSum,x,y); if(cnt<T) printf("\n"); } return 0; }
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