題目

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

題意

輸入序列元素個數並依次輸入元素，輸出子序列最大的和以及開始值和結束值。

分析

sum為最大和，temp為臨時最大和，lindex和rindex為所求的子序列的下標，tempindex標記l的臨時下標。temp = temp + v[i]，當temp比sum大，就更新sum的值、lindex和rindex的值；當temp < 0，應捨棄temp < 0前面的內容然後令temp = 0，並且同時更新l的臨時值tempindex。對於所有的值都為負數的情況要輸出0，第一個值，最後一個值，所以在輸入的時候用flag判斷是不是所有的數字都是小於0的。

程式碼 

#include <iostream>
#include <vector>
using namespace std;

int main() {
    int n;
    scanf("%d", &n);
    vector<int> v(n);
    int lindex = 0, rindex = n - 1, sum = -1, temp = 0, tempindex = 0;
    for (int i = 0; i < n; i++) {
        scanf("%d", &v[i]);
        temp = temp + v[i];
        if (temp < 0) {
            temp = 0;
            tempindex = i + 1;
        } else if (temp > sum) {
            sum = temp;
            lindex = tempindex;
            rindex = i;
        }
    }
    if (sum < 0) sum = 0;
    printf("%d %d %d", sum, v[lindex], v[rindex]);
    return 0;
}

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作者：柳婼 
來源：CSDN 
原文：https://blog.csdn.net/liuchuo/article/details/52144554