Three Parts of the Array(CF-1006C)

本文介绍了一种算法问题,即如何将一个整数数组分成三个连续的子数组,使得首尾两个子数组的和相等并且尽可能大。通过使用双指针技术优化原始的暴力解法,最终实现了高效的解决方案。

Problem Description

You are given an array d1,d2,…,dn consisting of nn integer numbers.

Your task is to split this array into three parts (some of which may be empty) in such a way that each element of the array belongs to exactly one of the three parts, and each of the parts forms a consecutive contiguous subsegment (possibly, empty) of the original array.

Let the sum of elements of the first part be sum1, the sum of elements of the second part be sum2 and the sum of elements of the third part be sum3. Among all possible ways to split the array you have to choose a way such that sum1=sum3 and sum1 is maximum possible.

More formally, if the first part of the array contains a elements, the second part of the array contains b elements and the third part contains c elements, then:

sum1=∑(1≤i≤a)di,
sum2=∑(a+1≤i≤a+b)di,
sum3=∑(a+b+1≤i≤a+b+c)di.
The sum of an empty array is 0.

Your task is to find a way to split the array such that sum1=sum3 and sum1 is maximum possible.

Input

The first line of the input contains one integer nn (1≤n≤2⋅10^5) — the number of elements in the array d.

The second line of the input contains nn integers d1,d2,…,dn (1≤di≤10^9) — the elements of the array d.

Output

Print a single integer — the maximum possible value of sum1, considering that the condition sum1=sum3 must be met.

Obviously, at least one valid way to split the array exists (use a=c=0 and b=n).

Examples

Input

5
1 3 1 1 4

Output

5

Input

5
1 3 2 1 4

Output

4

Input

3
4 1 2

Output

0

Note

In the first example there is only one possible splitting which maximizes sum1: [1,3,1],[ ],[1,4].

In the second example the only way to have sum1=4 is: [1,3],[2,1],[4].

In the third example there is only one way to split the array: [ ],[4,1,2],[ ].

题意:给出 n 个值,将这个数组分成三部分,sum1,sum2,sum3,可以为空,要求 sum1 = sum3 且 sum1 最大,求 sum1 的值

思路:

一开始用两个数组存从前往后与从后往前的和,然后双重循环暴力解决,结果超时了。。。

然后用了双重指针,分别指向第一个和最后一个,再分别记录从左到右与从右到左的和,然后通过移动指针来不断比较两个和,如果相等就把这个值记录下来,不断更新,直到左指针大于等于右指针

Source Program

#include<iostream>
#include<cstdio>
#include<cstring>
#include<cmath>
#include<algorithm>
#include<string>
#include<cstdlib>
#include<queue>
#include<set>
#include<map>
#include<stack>
#include<ctime>
#include<vector>
#define INF 0x3f3f3f3f
#define PI acos(-1.0)
#define N 1000001
#define MOD 123
#define E 1e-6
using namespace std;
long long a[N];
int main()
{
    int n;
    while(scanf("%d",&n)!=EOF)
    {
        for(int i=1;i<=n;i++)
            scanf("%d",&a[i]);

        long long head=1,tail=n;
        long long sum1=0,sum2=0;
        long long maxx=0;
        while(head<=tail)
        {
            if(sum1>sum2)
            {
                sum2+=a[tail];
                tail--;
            }
            else if(sum2>sum1)
            {
                sum1+=a[head];
                head++;
            }

            if(sum1==sum2)
            {
                maxx=max(maxx,sum1);
                sum1+=a[head];
                head++;
            }
        }
        printf("%lld\n",maxx);
    }

    return 0;
}

 

# -*- coding: utf-8 -*- from abaqus import * from abaqusConstants import * from caeModules import * from odbAccess import * import math import csv import os import numpy as np from scipy.stats import qmc def run_fem_simulation(params): try: tool_position = params['tool_position'] tool_step = params['tool_step'] ae = params['ae'] R = params['R'] # ---------------几何参数定义---------------- ap = 10.0 # 轴向切深 ae = 3.0 # 径向切深 ft = 0.5 # 每齿进给量 min_mesh = 0.5 # 切削区网格尺寸 max_mesh = 3.0 # 非切削区网格尺寸 # ---------------材料参数定义---------------- length = 120.0 # 工件长度(X方向) width = 60.0 # 工件宽度(Z方向) depth = 5.0 # 工件厚度(Y方向) material_name = 'TC4' E = 113800.0 # 弹性模量 (MPa) nu = 0.33 # 泊松比 density = 4.43e-6 # 密度 (kg/mm³) # ---------------刀具参数定义---------------- R = 6.0 # 刀具半径 helix_angle1 = 38 # 螺旋角1,单位:度 helix_angle2 = 41 E_tool = 2.1e5 # MPa I = math.pi * R ** 4 / 4 # 圆截面惯性矩 # ---------------切削力系数------------------ kt1, kte1 = 2026.48, 7.16 # 切向力系数 kn1, kne1 = 972.23, 16.99 # 法向力系数 ka1, kae1 = 764.08, 0.51 # 轴向力系数 kt2, kte2 = 2294.84, 10.69 # 切向力系数 kn2, kne2 = 988.74, 18.20 # 法向力系数 ka2, kae2 = 1015.45, 1.39 # 轴向力系数 N = 4 # 刀具齿数 omega = 5000 # 主轴转速 (rpm) steps = 64 # 旋转步数 phis = math.pi / 2 - math.acos(1 - ae / R) phie = math.pi / 2 convergence_threshold = 0.1 # 收敛阈值 model_name = 'Model-%d-%d' % (tool_position, tool_step) if model_name in mdb.models.keys(): del mdb.models[model_name] myModel = mdb.Model(name=model_name) # ---------------几何建模--------------------- # Part创建 mySketch = myModel.ConstrainedSketch(name='sketch', sheetSize=200) mySketch.rectangle((0, 0), (length, depth)) myPart = myModel.Part(name='WorkPiece', dimensionality=THREE_D, type=DEFORMABLE_BODY) myPart.BaseSolidExtrude(sketch=mySketch, depth=width) # 分割工件(用于不同区域网格划分) datum = myPart.DatumPlaneByPrincipalPlane(principalPlane=XYPLANE, offset=width / 2) myPart.PartitionCellByDatumPlane( datumPlane=myPart.datums[datum.id], cells=myPart.cells.getSequenceFromMask(mask=('[#1 ]',), ) ) # ---------------网格划分--------------------- # 切削区域(上半部分)精细网格 region_edges = myPart.edges.getByBoundingBox( xMin=-1e-5, xMax=length + 1e-5, yMin=-1e-5, yMax=depth + 1e-5, zMin=width / 2 - 1e-5, zMax=width + 1e-5 ) myPart.seedEdgeBySize(edges=region_edges, size=min_mesh, constraint=FINER) # 非切削区域(下半部分)粗网格 other_edges = myPart.edges.getByBoundingBox( xMin=-1e-5, xMax=length + 1e-5, yMin=-1e-5, yMax=depth + 1e-5, zMin=-1e-5, zMax=width / 2 + 1e-5 ) myPart.seedEdgeBySize(edges=other_edges, size=max_mesh, constraint=FINER) myPart.generateMesh() # ---------------材料定义--------------------- myMaterial = myModel.Material(name=material_name) myMaterial.Density(table=((density,),)) myMaterial.Elastic(table=((E, nu),)) # 截面属性 mySection = myModel.HomogeneousSolidSection(name='Section', material=material_name) region = myPart.Set(cells=myPart.cells[:], name='AllCells') myPart.SectionAssignment(region=region, sectionName='Section') # ---------------装配体操作------------------- myAssembly = myModel.rootAssembly instance_name = 'WorkPiece-Instance' myInstance = myAssembly.Instance(name=instance_name, part=myPart, dependent=ON) # ---------------边界条件设置----------------- # 固定底面(Z=0) # 选择在 xz 平面上的所有节点 nodes = myInstance.nodes fixed_nodes = nodes.getByBoundingBox(xMin=-1e-05, xMax=length, yMin=-1e-05, yMax=depth, zMin=-1e-05, zMax=1e-05) fixed_node_set = myAssembly.Set(nodes=fixed_nodes, name='FixedNodeSet' ) myModel.DisplacementBC(name='BC-FIX', createStepName='Initial', region=fixed_node_set, u1=0.0, u2=0.0, u3=0.0 ) # ---------------分析步设置------------------- if tool_position > 1: myModel.StaticStep(name='Step-del', previous='Initial', maxNumInc=200, timePeriod=1e-05, initialInc=1e-10, minInc=1e-10, maxInc=1e-05 ) myModel.StaticStep(name='Step-1', previous='Step-del', nlgeom=ON, maxNumInc=200, timePeriod=0.1, initialInc=1e-05, minInc=1e-05, maxInc=1e-02 ) else: myModel.StaticStep(name='Step-1', previous='Initial', nlgeom=ON, maxNumInc=200, timePeriod=0.1, initialInc=1e-05, minInc=1e-05, maxInc=1e-02 ) ###---------------------------------------------创建被切削区域集合----------------------------------------------------- # 切削区节点坐标 xmin = -1e-05 xmax = length ymin = -1e-05 ymax = ae + 1e-05 zmin = width - ap + 1e-05 zmax = width + 1e-05 # 创建被切削节点集合 nodes = myInstance.nodes milling_nodes = nodes.getByBoundingBox(xMin=xmin, xMax=xmax, yMin=ymin, yMax=ymax, zMin=zmin, zMax=zmax) node_set_name = 'MillingNodes' myAssembly.Set(nodes=milling_nodes, name=node_set_name) print(f'Created node set [{node_set_name}] containing {len(milling_nodes)} nodes') # 创建被切削单元集合 elements = myInstance.elements milling_elements = elements.getByBoundingBox(xMin=xmin, xMax=xmax + min_mesh, yMin=ymin, yMax=ymax, zMin=zmin - min_mesh, zMax=zmax) element_set_name = 'MillingElements' myAssembly.Set(elements=milling_elements, name=element_set_name) print(f'Created element set [{element_set_name}] containing {len(milling_elements)} elements') #生死单元单元格集合 milling_cells = milling_elements.getByBoundingBox(xMin=- 1e-5, xMax=(tool_position - 1) * R + 1e-5, yMin=ymin, yMax=ymax, zMin=zmin - min_mesh, zMax=zmax) removed_name = f'remove-P{tool_position}' myAssembly.Set(elements=milling_cells, name=removed_name) print(f'Created removed feature set [{removed_name}] containing {len(milling_cells)} elements') #变形节点集合 deformation_nodes = nodes.getByBoundingBox(xMin=(tool_position - 1) * R - min_mesh/2, xMax=(tool_position - 1) * R + min_mesh/2, yMin=ae - min_mesh + min_mesh/2, yMax=ae + min_mesh - min_mesh/2, zMin=width - ap + tool_step * min_mesh - min_mesh/2, zMax=width - ap + tool_step * min_mesh + min_mesh/2) if deformation_nodes: deformation_set_name = f'DEFORMATION-P{tool_position}-M{tool_step}' myAssembly.Set(nodes=deformation_nodes, name=deformation_set_name) print(f'Created deformation set [{deformation_set_name}] with {len(deformation_nodes)} nodes') else: print(f'[Warning] No deformation nodes found for tool position {tool_position}') ###----------------------------------------------计算并施加载荷--------------------------------------------------------- convergence_threshold = 0.2 displacement = 0 previous_ae = 0 iteration_number = 1 if tool_position % 2 == 1: helix_angle = helix_angle1 else: helix_angle = helix_angle2 dphi = math.pi * 2 / steps if helix_angle != 0: db = R * dphi / math.tan(math.radians(helix_angle)) else: db = ap / steps steps_axial = int(ap / db + 1) milling_set = {} for node in milling_nodes: node_id = node.label node_x, node_y, node_z = node.coordinates milling_set[node_id] = (node_x, node_y, node_z) loaded_node_coords = [] # === 计算所有齿中底部微元(cnt4=0)的最小切出步 === dphi = math.pi * 2 / steps # 旋转步长 min_exit_step = steps # 初始化为最大值 for cnt3 in range(N): # 计算当前齿底部微元切出所需步数 phia_needed = math.pi / 2 - phis - cnt3 * 2 * math.pi / N # 调整phia_needed到0-2π范围内 while phia_needed < 0: phia_needed += 2 * math.pi while phia_needed >= 2 * math.pi: phia_needed -= 2 * math.pi # 计算切出步数 cnt1_exit = math.ceil(phia_needed / dphi) # 更新最小切出步 if cnt1_exit < min_exit_step: min_exit_step = cnt1_exit while abs(ae - previous_ae) > convergence_threshold: Fy_total = [0.0] * steps_axial zj_list = [width - ap + j * db for j in range(steps_axial)] # 每个cnt4对应的Z轴坐标 delta_y_current = [0.0] * steps_axial # 当前轮的刀具变形,初始化为0 loaded_node_coords = [] # 清空加载节点坐标 for cnt1 in range(steps): if cnt1 == (min_exit_step - 1) + tool_step: for cnt3 in range(N): if cnt3 in [0, 2]: # 齿编号0和2使用第一组系数 kt, kte = kt1, kte1 kn, kne = kn1, kne1 ka, kae = ka1, kae1 else: # 齿编号1和3使用第二组系数 kt, kte = kt2, kte2 kn, kne = kn2, kne2 ka, kae = ka2, kae2 for cnt4 in range(steps_axial): phia = phis + cnt1 * dphi + cnt3 * 2 * math.pi / N - cnt4 * db * math.tan( math.radians(helix_angle)) / R phia = phia % (2 * math.pi) if phis <= phia <= phie: h = ft * math.sin(phia) Ft = kt * h * db + kte * db Fn = kn * h * db + kne * db Fa = ka * h * db + kae * db else: Ft, Fn, Fa = 0, 0, 0 # 将切削力分解到直角坐标系 Fx = -Ft * math.cos(phia) - Fn * math.sin(phia) Fy = Ft * math.sin(phia) - Fn * math.cos(phia) Fz = Fa # 累加Fy Fy_total[cnt4] += Fy for i in range(int(length / R) - 1): # 计算刀具坐标系切削微元位置 micro_x = R * math.cos(phia) + (tool_position - 1) * R micro_y = R * math.sin(phia) - (depth - ae) - delta_y_current[cnt4] micro_z = width - ap + cnt4 * db # 找到最近的节点 min_distance = float('inf') nearest_node = None for node_id, (node_x, node_y, node_z) in milling_set.items(): distance = math.sqrt( (micro_x - node_x) ** 2 + (micro_y - node_y) ** 2 + (micro_z - node_z) ** 2) if distance < min_distance: min_distance = distance nearest_node = node_id # 创建载荷 if nearest_node is not None and (Fx != 0 or Fy != 0 or Fz != 0): node = milling_nodes.sequenceFromLabels((nearest_node,)) node_name = 'Load-' + str(cnt1) + '-' + str(cnt3) + '-' + str(cnt4) load_name = 'Force-' + str(cnt1) + '-' + str(cnt3) + '-' + str(cnt4) node_set = myAssembly.Set(nodes=node, name=node_name) myModel.ConcentratedForce(name=load_name, createStepName='Step-1', region=node_set, cf1=Fx, cf2=Fy, cf3=Fz) node_x, node_y, node_z = milling_set[nearest_node] loaded_node_coords.append((node_x, node_y, node_z)) # 创建参考点 adjusted_point = (micro_x, micro_y, micro_z) reference_point_name = 'RP-' + str(cnt1) + '-' + str(cnt3) + '-' + str(cnt4) reference_point = myAssembly.ReferencePoint(point=adjusted_point) # 刀具变形计算 delta_y_new = [] # 创建新列表存储本轮的变形计算结果 for j in range(steps_axial): zj = zj_list[j] delta = 0.0 for jp in range(steps_axial): zjp = zj_list[jp] if zj <= zjp: K = zjp ** 2 * (3 * zj - zjp) / (6 * E_tool * I) else: K = zj ** 2 * (3 * zjp - zj) / (6 * E_tool * I) delta += K * Fy_total[jp] delta_y_new.append(delta) # 更新delta_y_current用于下一次迭代(只在有计算值时更新) if delta_y_new: # 确保列表不为空 delta_y_current = delta_y_new ###------------------------------------------------------生死单元------------------------------------------------ if tool_position > 1: intname = 'Int-' + str(tool_position) stepname = 'Step-del' element_name = removed_name int_region = myAssembly.sets[element_name] myModel.ModelChange(name=intname, createStepName=stepname, region=int_region, regionType=ELEMENTS, activeInStep=False, includeStrain=False ) ###-------------------------------------------------------创建作业--------------------------------------------------- job_name = f'Model-{tool_position}-{tool_step}-{iteration_number}' myJob = mdb.Job(name=job_name, model=model_name, type=ANALYSIS, numCpus=24, numDomains=24) myJob.submit() mdb.jobs[job_name].waitForCompletion() ###-----------------------------------------------------打开ODB文件-------------------------------------------------- try: odb = openOdb(path=job_name + '.odb') step_name = 'Step-1' displacement_field = odb.steps[step_name].frames[-1].fieldOutputs['U'] instance_name = 'WORKPIECE-INSTANCE' instance = odb.rootAssembly.instances[instance_name] deformation_name = f'DEFORMATION-P{tool_position}-M{tool_step}' if deformation_name in odb.rootAssembly.nodeSets: region = odb.rootAssembly.nodeSets[deformation_name] displacement_subset = displacement_field.getSubset(region=region) displacement = displacement_subset.values[0].data[2] else: print(f"[Critical] Node set {deformation_name} missing in ODB!") displacement = 0 # 默认值或终止 print(f'ae={ae},displacement={displacement}') except Exception as e: print(f"Error reading ODB: {str(e)}") displacement = 0 finally: odb.close() pre_ae = ae ae -= abs(displacement) ae = (ae + previous_ae)/2 previous_ae = pre_ae if iteration_number > 10: break else: iteration_number += 1 final_displacement = displacement # 从ODB获取最终位移 final_ae = ae # 最终径向切深 print('final ae is:', final_ae) print('final displacement is:', final_displacement) return { 'displacement': final_displacement, 'final_ae': final_ae, 'status': 'success', 'message': 'Simulation completed successfully' } except Exception as e: return { 'status': 'error', 'message': str(e), 'displacement': None, 'final_ae': None } def generate_parameters(samples): """生成拉丁超立方采样参数组合""" param_ranges = { 'tool_position': (1, 19), 'tool_step': (1, 11) } # 拉丁超立方采样 sampler = qmc.LatinHypercube(d=len(param_ranges)) sample_data = sampler.random(n=samples) # 构造参数列表 params_list = [] for sample in qmc.scale(sample_data, [v[0] for v in param_ranges.values()], [v[1] for v in param_ranges.values()]): params = { 'tool_position': int(round(sample[0])), 'tool_step': int(round(sample[1])), 'ae': 3.0, # 固定值 'R': 5.0 # 固定值 } params_list.append(params) return params_list # 数据保存模块 class DataRecorder: def __init__(self, filename="simulation_data.csv"): self.filename = filename self._init_file() def _init_file(self): """初始化数据文件""" if not os.path.exists(self.filename): with open(self.filename, 'w', newline='') as f: writer = csv.writer(f) writer.writerow([ 'tool_position', 'tool_step', 'ae_input', 'R_input', 'displacement', 'final_ae', 'status' ]) def save_record(self, params, result): """保存单条记录""" record = { 'tool_position': params['tool_position'], 'tool_step': params['tool_step'], 'ae_input': params['ae'], 'R_input': params['R'], 'displacement': result.get('displacement', None), 'final_ae': result.get('final_ae', None), 'status': result['status'] } with open(self.filename, 'a', newline='') as f: writer = csv.DictWriter(f, fieldnames=record.keys()) writer.writerow(record) if __name__ == '__main__': # 初始化数据记录器 recorder = DataRecorder() # 生成参数组合 param_combinations = generate_parameters(samples=200) # 执行参数扫描 for idx, params in enumerate(param_combinations,1): print(f"\n 正在执行参数组合 {idx}/{len(param_combinations)}") print(f" 刀具位置: {params['tool_position']}") print(f" 刀具旋转步: {params['tool_step']}") print(f" 径向切深: {params['ae']}mm") print(f" 刀具半径: {params['R']}mm") # 执行仿真 result = run_fem_simulation(params) # 处理结果 if result['status'] == 'success': print(f"成功完成: 位移={result['displacement']}mm, 最终ae={result['final_ae']}mm") else: print(f"执行失败: {result['message']}") # 保存数据 recorder.save_record(params, result) print("\n所有参数组合执行完成!") print(f"数据文件已保存至: {os.path.abspath(recorder.filename)}") 以上是我的py代码,在abaqus中运行速度特别缓慢
最新发布
07-22
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