poj2593 Max Sequence（求兩個不相交最大欄位和）

標籤：數學   poj   遍曆   

轉載請註明出處：http://blog.csdn.net/u012860063?viewmode=contents

題目連結：http://poj.org/problem?id=2593

Description

Give you N integers a1, a2 ... aN (|ai| <=1000, 1 <= i <= N). 

You should output S. 

Input

The input will consist of several test cases. For each test case, one integer N (2 <= N <= 100000) is given in the first line. Second line contains N integers. The input is terminated by a single line with N = 0.

Output

For each test of the input, print a line containing S.

Sample Input

5-5 9 -5 11 200

Sample Output

40

 思想：對於資料a[]，從左向右依次求解以a[i]結尾的最大子段和b[i]，  然後，從右向左遍曆，求a[i]右邊（包括a[i]）的最大子段和sum，輸出sum+b[i-1]的  最大值。

代碼如下：

#include <iostream>using namespace std;#define INF 0x3fffffff#define M 100000+17int a[M],b[M];int main(){int n,i;while(cin >> n && n){int sum = 0, MAX = -INF;for(i = 1; i <= n; i++){cin >> a[i];sum+=a[i];if(sum > MAX){MAX = sum;}b[i] = MAX;if(sum < 0){sum = 0;}}MAX = -INF;sum = 0;int ans = MAX, t;for(i = n; i > 1; i--){sum+=a[i];if(sum > MAX){MAX = sum;}t = MAX + b[i-1];if(t > ans){ans = t;}if(sum < 0){sum = 0;}}cout<<ans<<endl;}return 0;}