1.遞迴

該方法由書上提供，比較好理解：給定一個數組，從中間劃分成兩個陣列[1,mid]，[mid+1,end]；a.位於左半邊 b.位於右半邊 c.跨越兩邊。求兩邊最大子序列時可遞迴求解，求跨越兩邊的子序列時分別從mid、mid+1出發，求得left_sum和right_sum，相加即為跨越兩邊的最大子序列和。

程式碼：

#include <stdio.h>
#include <stdlib.h>

int Find_Mid_Max(int* q,int start,int end) {
    int mid = (start + end) / 2;
    int
 
 left_sum = 0;
    int right_sum = 0;
    int sum = 0;
    int i;
    for (i = mid;i > 0;i--) {
        sum += q[i];
        if (sum > left_sum)
            left_sum = sum;
    }
    sum = 0;
    for (i = mid+1;i <=end;i++) {
        sum += q[i];
        if (sum > right_sum)
            right_sum 
 
= sum;
    }
    return left_sum + right_sum;
}

int Find_Max(int* q, int start, int end) {
    int maxsum = 0;
    if (start == end) {
        if (q[end] > maxsum)
            maxsum = q[end];
        return maxsum;
    }
    int mid = (start + end) / 2;
    int left=Find_Max(q, start, mid);
    int
 
 right = Find_Max(q, mid + 1, end);
    int across = Find_Mid_Max(q, start, end);
    if (left > right && left > across)
        maxsum = left;
    else if (right > across)
        maxsum = right;
    else
        maxsum = across;
    return maxsum;
}

int main() {
    int k;
    if (scanf("%d", &k) == 0){}
    int* q = (int*)malloc(sizeof(int) *(k+1));
    int i;
    for (i = 1;i <= k;i++) {
        if(scanf("%d",&q[i])==0){}
    }
    int max=Find_Max(q, 1, k);
    printf("%d", max);
    return 0;
}