PTA-01-复杂度2 Maximum Subsequence Sum

Given a sequence of K integers { N​1​​, N​2​​, …, N​K​​ }. A continuous subsequence is defined to be { N​i​​, N​i+1​​, …, N​j​​ } 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

思路

与上一篇最大子序列的思路基本一致，该题只要把子序列最大值的索引存下来，最后做一个遍历，找到最小索引值，则得到最后答案

int fun1(int num,int *p){
	int max = 0;
	int cur = 0;
	int minpos = 0;
	int maxpos = 0;
	int flag = 1;
	for(int i = 0;i < num;i++){
		cur += p[i];
		if( cur > max){
			max = cur;
			maxpos = i;
		}else if(cur < 0){
			cur = 0;
		}
		if(p[i]>=0){
			flag = 0;
		}
	}
	int tmp = 0;
	for(int i = maxpos;i >= 0;i--){
		tmp = tmp + p[i];
		if(tmp == max){
			minpos = i;
		}
	}
	if(max > 0){
		cout<<max<<' '<<p[minpos]<<' '<<p[maxpos]<<endl;
	}
	else{
        if(flag)
        {
		    cout<<"0 0 0"<<endl;
	    }
		else{
            cout<<0<<' '<<p[0]<<' '<<p[num - 1]<<endl;
        }
	}
	return 0;
}

源码