最大子序列和分治算法

#include<stdio.h>
#include<iostream>
#include<string>
#include<string.h>
#include<algorithm>
#include<vector>
#include<time.h>
#include<queue>
#include<stack>
#include<iterator>
#include<math.h>
#include<stdlib.h>
#include<limits.h>
#include<map>
#include<memory.h>
//#define ONLINE_JUDGE
#define eps 1e-8
#define INF 0x7fffffff                                          //INT_MAX
#define inf 0x3f3f3f3f                                          //int??????????????????
#define FOR(i,a) for((i)=0;i<(a);(i)++)                          //[i,a);
#define MEM(a) (memset((a),0,sizeof(a)))
#define sfs(a) scanf("%s",a)
#define sf(a) scanf("%d",&a)
#define sfI(a) scanf("%I64d",&a)
#define pf(a) printf("%d\n",a)
#define pfI(a) printf("%I64d\n",a)
#define pfs(a) printf("%s\n",a)
#define sfd(a,b) scanf("%d%d",&a,&b)
#define sft(a,b,c)scanf("%d%d%d",&a,&b,&c)
#define for1(i,a,b) for(int i=(a);i<b;i++)
#define for2(i,a,b) for(int i=(a);i<=b;i++)
#define for3(i,a,b)for(int i=(b);i>=a;i--)
#define MEM1(a) memset(a,0,sizeof(a))
#define MEM2(a) memset(a,-1,sizeof(a))
#define LL __int64
const double PI = acos(-1.0);
template<class T> T gcd(T a, T b) { return b ? gcd(b, a % b) : a; }
template<class T> T lcm(T a, T b) { return a / gcd(a, b) * b; }
template<class T> inline T Min(T a, T b) { return a < b ? a : b; }
template<class T> inline T Max(T a, T b) { return a > b ? a : b; }
using namespace std;
template<class T>
T Mint(T a, T b, T c) {
if (a>b) {
if (c>b)
return b;
return c;
}
if (c>a)
return a;
return c;
}
template<class T>
T Maxt(T a, T b, T c) {
if (a>b) {
if (c>a)
return c;
return a;
}
else if (c > b)
return c;
return b;
}

int FindCrossMid(int low, int high, int mid, int A[]) {
int leftsum = INT_MIN;//左边最大和
int sum1 = 0;
int leftindex;//取左边最大和时数组的下标
for (int i = mid; i >= low; i--) {
sum1 += A[i];
if (sum1>leftsum) {
leftsum = sum1;//更新最大和
leftindex = i;//更新数组下标
}
}
int rightsum = INT_MIN;//右边最大和
int sum2 = 0;
int rightindex;//取右边最大和时数组的下标
for (int i = mid+1; i <= high; i++) {
sum2 += A[i];
if (sum2>rightsum) {
rightsum = sum2;//更新最大和
rightindex = i;//更新数组下标
}
}
return leftsum + rightsum;//返回最大和
}

int FindMaxSubsequence(int low, int high, int A[]) {
if (high == low)
return A[low];
else {
int mid = (low + high) / 2;
int leftsum, rightsum, crosssum;
leftsum = FindMaxSubsequence(low, mid, A);//左半部最大子序列和
rightsum = FindMaxSubsequence(mid+1, high, A);//右半部最大子序列和
crosssum = FindCrossMid(low, high, mid, A);//中间最大子序列和
if (leftsum>crosssum&&leftsum>rightsum)
return leftsum;
else if (rightsum>leftsum&&rightsum>crosssum)
return rightsum;
else
return crosssum;
}
}

int main() {
int A[100];
int n;
sf(n);
for1(i, 0, n)
sf(A[i]);
cout << FindMaxSubsequence(0, n-1, A) << endl;
system("pause");
return 0;
}