01-复杂度2 Maximum Subsequence Sum （25 分）
Given a sequence of K integers { N1, N2, …, NK }. A continuous subsequence is defined to be { Ni, Ni+1, …, Nj } where 1≤i≤j≤K. The Maximum Subsequence is the continuous subsequence which has the largest sum of its elements. For example, given sequence { -2, 11, -4, 13, -5, -2 }, its maximum subsequence is { 11, -4, 13 } with the largest sum being 20.
Now you are supposed to find the largest sum, together with the first and the last numbers of the maximum subsequence.
Input Specification:
Each input file contains one test case. Each case occupies two lines. The first line contains a positive integer K (≤10000). The second line contains K numbers, separated by a space.
Output Specification:
For each test case, output in one line the largest sum, together with the first and the last numbers of the maximum subsequence. The numbers must be separated by one space, but there must be no extra space at the end of a line. In case that the maximum subsequence is not unique, output the one with the smallest indices i and j (as shown by the sample case). If all the K numbers are negative, then its maximum sum is defined to be 0, and you are supposed to output the first and the last numbers of the whole sequence.
Sample Input:
10
-10 1 2 3 4 -5 -23 3 7 -21
Sample Output:
10 1 4
我这渣渣英语，真的。。。。搞了一早上，以为输出的是：最大序列和 下标 下标；其实，输出的是：最大序列和 下标对应的值 下标对应的值。
这个里面注意的是，如果全部是负数，应该输出0 a[0] a[n-1]，如果有负数有0，应该输出0 0 0
具体思路：设置一个flag，如果在向后加序列的时候出现和为负数，那就从头开始加，开头的下标就要从下一个下标开始，然后每次符合要求都记录这次的start和end
#include <stdio.h>
int main()
{
int n, i, flag=0;
scanf("%d", &n);
int a[n];
for(i=0;i<n;i++){
scanf("%d", &a[i]);
}
int maxNum=0,ThisNum=0, start=0, Thisstart=0, end=n-1;
for(i=0;i<n;i++){
ThisNum+=a[i];
if(flag==1){
Thisstart=i;
flag=0;
}
if(ThisNum>maxNum ||(ThisNum>=maxNum && maxNum==0)){
// 符合条件
// ThisNum>=maxNum && maxNum==0 这个是为了保证有负数有0的时候输出0 0 0
maxNum=ThisNum;
start = Thisstart;
end = i;
}
else if(ThisNum<0){
// 不符合条件
flag=1;
ThisNum=0;
}
}
printf("%d %d %d", maxNum, a[start], a[end]);
return 0;
}
/*
10
-10 1 2 3 4 -5 23 3 7 -21
10
-10 -1 -2 -1 0 -5 -23 -3 -7 -21
*/