最大子数组问题的三种方法：分治法、暴力法和非递归方法

参考算法导论及其习题，直接上代码

// P38_MaxSubArray.cpp : Defines the entry point for the console application.
//

#include "stdafx.h"

#include 

using namespace std;

int main()
{
    // 分治法
    int calculateMaxSubArray(int arr[], int start, int end);
    int calculateMaxSubArrayCrossMid(int arr[], int start, int mid, int end);

    // 暴力法
    int calculateMaxSubArray_BaoLi(int arr[], int start, int end);

    // 非递归方法
    int calculateMaxSubArray_NoDiGui(int arr[], int start, int end);

    int arr[] = {13, -3, -25, 20, -3, -16, -23, 18, 20, -7, 12, -5, -22, 15, -4, 7};
    // int arr[] = { -3, -2, -1, -2, -4, -5, -6, -7, -8, -89, -10, -11, -12, -13 };

    int n = sizeof(arr) / sizeof(int);

    cout << n << endl;

    int max = calculateMaxSubArray(arr, 0, n);
    cout << "分治法 " << max << endl;

    max = calculateMaxSubArray_BaoLi(arr, 0, n);
    cout << "暴力法 " << max << endl;

    max = calculateMaxSubArray_NoDiGui(arr, 0, n);
    cout << "非递归法 " << max << endl;

    return 0;
}

int calculateMaxSubArrayCrossMid(int arr[], int start, int mid, int end) {
    int left_sum = -10000, right_sum = -10000;
    int sum = 0;
    for (int i = mid - 1; i >= 0; i--) {
        sum += arr[i];
        if (left_sum < sum) {
            left_sum = sum;
        }
    }

    sum = 0;
    for (int i = mid; i < end; i++) {
        sum += arr[i];
        if (right_sum < sum) {
            right_sum = sum;
        }
    }

    return left_sum + right_sum;
}

int calculateMaxSubArray(int arr[], int start, int end) {
    if (start + 1 == end) {
        return arr[start];
    }
    int mid = (start + end) / 2;
    int m1 = calculateMaxSubArray(arr, start, mid);
    int m2 = calculateMaxSubArray(arr, mid, end);
    int m3 = calculateMaxSubArrayCrossMid(arr, start, mid, end);
    m2 = m2 > m1 ? m2 : m1;
    return m3 > m2 ? m3 : m2;
}

int calculateMaxSubArray_BaoLi(int arr[], int start, int end) {
    int max = -10000;
    int sum = 0;
    for (int i = start; i < end; i++) {
        for (int j = i; j < end; j++) {
            sum = 0;
            for(int k = i; k <= j; k++){
                sum += arr[k];
            }
            if (sum > max) {
                max = sum;
            }
        }
    }

    return max;
}

int calculateMaxSubArray_NoDiGui(int arr[], int start, int end) {
    int s = start, e = 0, max = arr[0], sum = 0, right_sum = 0, sTmp = 0, eTmp = 0;

    for (int i = start + 1; i < end; i++) {
        right_sum = -10000;
        sum = 0;
        for (int j = i; j >= s; j--) {
            sum += arr[j];
            if (sum > right_sum) {
                right_sum = sum;
                sTmp = j;
            }
        }
        eTmp = i;
        if (right_sum > max) {
            max = right_sum;
            s = sTmp;
            e = eTmp;
        }
    }

    cout << s << ", " << e << endl;
    return max;
}