UVa #714 Copying Books (例题8-10)

本文解析了一道UVa在线编程挑战题目,强调了保持原始书本顺序的重要性,并通过EM算法和拉格朗日乘子法等概念进行了优化讨论。文章分享了一个C++实现示例,该示例使用二分查找来确定最优解,并详细展示了如何分配任务以达到目标条件。

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最大值最小化,第一反应是Convex Optimization,想起了拉格朗日乘子法和对偶性哈哈哈


Rujia这个不断压低上限的做法,又让我想起了EM算法(其实完全不是一个东西吧)


这道题需要注意几点:

1、书的顺序是不能改变的。

2、RE有可能是因为整型溢出。每道题都必须仔细检查所有可能溢出的地方

3、好好照顾循环的出入口、妥善处理循环跳出后还没有处理的数据(例如归并排序的循环结束后)


Run Time: 0.016s

#define UVa  "LT8-10.714.cpp"
char fileIn[30] = UVa, fileOut[30] = UVa;

#include<cstring>
#include<cstdio>
#include<vector>
#include<algorithm>

using namespace std;


//Global Variables. Reset upon Each Case!
const long long  maxn = 1000;
long long  m, k;
long long  books[maxn];
/////

int P(long long x) {
    long long groups = 1;
    long long sum = 0;
    for(long long  i = 0; i < m; i ++) {
        if(books[i] > x) return 0;
        if(sum + books[i] > x) {
            groups ++;
            sum = 0;
        }
        sum += books[i];
    }
    if(sum > x) {
        groups ++;
    }
    if(groups > k) return 0;
    return 1;
}

int main() {

    int N;
    scanf("%d", &N);
    for(int kase = 0; kase < N; kase ++) {
        scanf("%d%d", &m, &k);

        for(long long i = 0; i < m; i ++) scanf("%d", &books[i]);

        long long l = 0;
        long long r = 5000000010L;
        while(l < r) {
            long long mid = l + (r-l)/2;
            if(P(mid)) {
                r = mid;
            }
            else {
                l = mid + 1;
            }
        }

        vector<int> ans[maxn];              //one vector per scriber
        long long sum = 0;
        long long cur_scriber = k-1;
        long long cur_book;
        for(cur_book = m-1; cur_book >= 0; cur_book --) {
            if(sum + books[cur_book] > l) {
                sum = 0;
                cur_scriber --;
            }
            if(cur_book == cur_scriber) {       //one book per scriber.
                for(int i = 0; i <= cur_book; i ++) ans[i].push_back(books[i]);
                break;
            }
            ans[cur_scriber].push_back(books[cur_book]);
            sum += books[cur_book];
        }

        for(long long i = 0; i < k; i ++) {
            for(long long j = ans[i].size()-1; j >= 0; j --) {
                if(j != ans[i].size()-1) printf(" ");
                printf("%d", ans[i][j]);
            }
            if(i!=k-1)printf(" / ");
        }
        printf("\n");
    }
    return 0;
}


# Makefile for GeekOS kernel, userspace, and tools # Copyright (c) 2004,2005 David H. Hovemeyer <daveho@cs.umd.edu> # $Revision: 1.45 $ # This is free software. You are permitted to use, # redistribute, and modify it as specified in the file "COPYING". # Required software to build GeekOS: # - GNU Make (http://www.gnu.org/software/make) # - gcc 2.95.2 generating code for target (i386/ELF) and host platforms # - nasm (http://nasm.sourceforge.net) # - Perl5, AWK (any version), egrep # # Cygwin (http://cygwin.com) may be used to build GeekOS. # Make sure that gcc, binutils, nasm, and perl are installed. # NOTES: # - This makefile has been written carefully to work correctly # with the -j (parallel make) option. I regularly use "make -j 2" # to speed the build process on 2 processor systems. PROJECT_ROOT := .. VPATH := $(PROJECT_ROOT)/src # Figure out if we&#39;re compiling with cygwin, http://cygwin.com SYSTEM_NAME := $(shell uname -s) ifeq ($(findstring CYGWIN,$(SYSTEM_NAME)),CYGWIN) SYM_PFX := _ EXTRA_C_OPTS := -DNEED_UNDERSCORE -DGNU_WIN32 EXTRA_NASM_OPTS := -DNEED_UNDERSCORE NON_ELF_SYSTEM := yes EXTRA_CC_USER_OPTS := -Dmain=geekos_main endif # ---------------------------------------------------------------------- # Configuration - # Various options specifying how GeekOS should be built, # what source files to build, which user programs to build, # etc. This is generally the only section of the makefile # that will need to be modified. # ---------------------------------------------------------------------- # List of targets to build by default. # These targets encompass everything needed to boot # and run GeekOS. ALL_TARGETS := fd.img # Kernel source files KERNEL_C_SRCS := idt.c int.c trap.c irq.c io.c \ keyboard.c screen.c timer.c \ mem.c crc32.c \ gdt.c tss.c segment.c \ bget.c malloc.c \ synch.c kthread.c \ main.c # Kernel object files built from C source files KERNEL_C_OBJS := $(KERNEL_C_SRCS:%.c=geekos/%.o) # Kernel assembly files KERNEL_ASM_SRCS := lowlevel.asm # Kernel object files build from assembler source files KERNEL_ASM_OBJS := \ $(KERNEL_ASM_SRCS:%.asm=geekos/%.o) # All kernel object files KERNEL_OBJS := $(KERNEL_C_OBJS) \ $(KERNEL_ASM_OBJS) # Common library source files. # This library is linked into both the kernel and user programs. # It provides string functions and generic printf()-style # formatted output. COMMON_C_SRCS := fmtout.c string.c memmove.c # Common library object files. COMMON_C_OBJS := $(COMMON_C_SRCS:%.c=common/%.o) # Base address of kernel KERNEL_BASE_ADDR := 0x00010000 # Kernel entry point function KERNEL_ENTRY = $(SYM_PFX)Main # ---------------------------------------------------------------------- # Tools - # This section defines programs that are used to build GeekOS. # ---------------------------------------------------------------------- # Uncomment if cross compiling #TARGET_CC_PREFIX := i386-elf- # Target C compiler. gcc 2.95.2 or later should work. TARGET_CC := $(TARGET_CC_PREFIX)gcc # Host C compiler. This is used to compile programs to execute on # the host platform, not the target (x86) platform. On x86/ELF # systems, such as Linux and FreeBSD, it can generally be the same # as the target C compiler. HOST_CC := gcc # Target linker. GNU ld is probably to only one that will work. TARGET_LD := $(TARGET_CC_PREFIX)ld # Target archiver TARGET_AR := $(TARGET_CC_PREFIX)ar # Target ranlib TARGET_RANLIB := $(TARGET_CC_PREFIX)ranlib # Target nm TARGET_NM := $(TARGET_CC_PREFIX)nm # Target objcopy TARGET_OBJCOPY := $(TARGET_CC_PREFIX)objcopy # Nasm (http://nasm.sourceforge.net) NASM := nasm # Tool to build PFAT filesystem images. BUILDFAT := tools/builtFat.exe # Perl5 or later PERL := perl # Pad a file so its size is a multiple of some unit (i.e., sector size) PAD := $(PERL) $(PROJECT_ROOT)/scripts/pad # Create a file filled with zeroes. ZEROFILE := $(PERL) $(PROJECT_ROOT)/scripts/zerofile # Calculate size of file in sectors NUMSECS := $(PERL) $(PROJECT_ROOT)/scripts/numsecs # ---------------------------------------------------------------------- # Definitions - # Options passed to the tools. # ---------------------------------------------------------------------- # Flags used for all C source files GENERAL_OPTS := -O -Wall $(EXTRA_C_OPTS) CC_GENERAL_OPTS := $(GENERAL_OPTS) -Werror # Flags used for kernel C source files CC_KERNEL_OPTS := -g -DGEEKOS -I$(PROJECT_ROOT)/include # Flags user for kernel assembly files NASM_KERNEL_OPTS := -I$(PROJECT_ROOT)/src/geekos/ -f elf $(EXTRA_NASM_OPTS) # Flags used for common library and libc source files CC_USER_OPTS := -I$(PROJECT_ROOT)/include -I$(PROJECT_ROOT)/include/libc \ $(EXTRA_CC_USER_OPTS) # Flags passed to objcopy program (strip unnecessary sections from kernel.exe) OBJCOPY_FLAGS := -R .dynamic -R .note -R .comment # ---------------------------------------------------------------------- # Rules - # Describes how to compile the source files. # ---------------------------------------------------------------------- # Compilation of kernel C source files geekos/%.o : geekos/%.c $(TARGET_CC) -c $(CC_GENERAL_OPTS) $(CC_KERNEL_OPTS) $< -o geekos/$*.o # Compilation of kernel assembly source files geekos/%.o : geekos/%.asm $(NASM) $(NASM_KERNEL_OPTS) $< -o geekos/$*.o geekos/%.o : geekos/%.S $(TARGET_CC) -c $(CC_GENERAL_OPTS) $(CC_KERNEL_OPTS) $< -o geekos/$*.o # Compilation of common library C source files common/%.o : common/%.c $(TARGET_CC) -c $(CC_GENERAL_OPTS) $(CC_USER_OPTS) $< -o common/$*.o # ---------------------------------------------------------------------- # Targets - # Specifies files to be built # ---------------------------------------------------------------------- # Default target - see definition of ALL_TARGETS in Configuration section all : $(ALL_TARGETS) # Standard floppy image - just boots the kernel fd.img : geekos/fd_boot.bin geekos/setup.bin geekos/kernel.bin cat geekos/fd_boot.bin geekos/setup.bin geekos/kernel.bin > $@ # Floppy boot sector (first stage boot loader). geekos/fd_boot.bin : geekos/setup.bin geekos/kernel.bin $(PROJECT_ROOT)/src/geekos/fd_boot.asm $(NASM) -f bin \ -I$(PROJECT_ROOT)/src/geekos/ \ -DNUM_SETUP_SECTORS=`$(NUMSECS) geekos/setup.bin` \ -DNUM_KERN_SECTORS=`$(NUMSECS) geekos/kernel.bin` \ $(PROJECT_ROOT)/src/geekos/fd_boot.asm \ -o $@ # Setup program (second stage boot loader). geekos/setup.bin : geekos/kernel.exe $(PROJECT_ROOT)/src/geekos/setup.asm $(NASM) -f bin \ -I$(PROJECT_ROOT)/src/geekos/ \ -DENTRY_POINT=0x`egrep &#39;Main$$&#39; geekos/kernel.syms |awk &#39;{print $$1}&#39;` \ $(PROJECT_ROOT)/src/geekos/setup.asm \ -o $@ $(PAD) $@ 512 # Loadable (flat) kernel image. geekos/kernel.bin : geekos/kernel.exe $(TARGET_OBJCOPY) $(OBJCOPY_FLAGS) -S -O binary geekos/kernel.exe geekos/kernel.bin $(PAD) $@ 512 # The kernel executable and symbol map. geekos/kernel.exe : $(KERNEL_OBJS) $(COMMON_C_OBJS) $(TARGET_LD) -o geekos/kernel.exe -Ttext $(KERNEL_BASE_ADDR) -e $(KERNEL_ENTRY) \ $(KERNEL_OBJS) $(COMMON_C_OBJS) $(TARGET_NM) geekos/kernel.exe > geekos/kernel.syms # Clean build directories of generated files clean : for d in geekos common libc user tools; do \ (cd $$d && rm -f *); \ done # Build header file dependencies, so source files are recompiled when # header files they depend on are modified. depend : $(GENERATED_LIBC_SRCS) $(TARGET_CC) -M $(CC_GENERAL_OPTS) $(CC_KERNEL_OPTS) \ $(KERNEL_C_SRCS:%.c=$(PROJECT_ROOT)/src/geekos/%.c) \ | $(PERL) -n -e &#39;s,^(\S),geekos/$$1,;print&#39; \ > depend.mak $(TARGET_CC) -M $(CC_GENERAL_OPTS) $(CC_USER_OPTS) \ $(COMMON_C_SRCS:%.c=$(PROJECT_ROOT)/src/common/%.c) \ | $(PERL) -n -e &#39;s,^(\S),common/$$1,;print&#39; \ >> depend.mak # By default, there are no header file dependencies. depend.mak : touch $@ include depend.mak 在哪里修改
最新发布
05-30
### 解决方案 在编译 GeekOS 内核时出现的“variable ‘thread’ set but not used”错误,可以通过以下两种方式解决:修改源代码或调整 Makefile 中的编译器选项[^1]。 #### 修改源代码以消除警告 如果变量 `thread` 在函数中确实没有被使用,则可以采取以下方法之一来消除警告: ##### 方法 1:删除未使用的变量 如果变量 `thread` 不再需要,可以直接从代码中移除其定义和赋值操作。例如: ```c // 原始代码 struct Kernel_Thread *thread; thread = CreateKernelThread(...); // 修改后的代码 // 删除未使用的变量 thread ``` ##### 方法 2:显式声明变量未被使用 如果变量 `thread` 是为了调试或其他目的而存在,但当前不希望触发警告,可以通过 `(void)` 显式声明变量未被使用。例如: ```c struct Kernel_Thread *thread; thread = CreateKernelThread(...); (void)thread; // 显式声明变量未被使用 ``` ##### 方法 3:确保变量被实际使用 如果变量 `thread` 的定义和赋值是逻辑上必需的,则应确保其在后续代码中被正确使用。例如: ```c struct Kernel_Thread *thread; thread = CreateKernelThread(...); if (thread != NULL) { // 对 thread 进行操作 } ``` #### 调整 Makefile 编译器选项 如果不想修改源代码,可以通过调整 `Makefile` 中的编译器选项来禁用该警告。具体方法如下: ##### 方法 1:禁用特定警告 可以在 `CFLAGS` 中添加 `-Wno-unused-but-set-variable` 以禁用该警告。例如: ```makefile CFLAGS += -Wall -Werror -Wno-unused-but-set-variable ``` ##### 方法 2:将警告降级为非错误 如果仍然希望保留警告信息但不将其视为错误,可以移除 `-Werror` 选项。例如: ```makefile CFLAGS += -Wall ``` #### 示例代码与配置 以下是一个完整的示例,展示如何通过修改源代码或调整 Makefile 来解决该问题。 ##### 源代码修改示例 ```c #include "geekos/thread.h" void Main(void) { struct Kernel_Thread *thread; thread = CreateKernelThread(...); (void)thread; // 显式声明变量未被使用 } ``` ##### Makefile 配置示例 ```makefile CC = gcc CFLAGS = -Wall -Werror -Wno-unused-but-set-variable main: main.o $(CC) $(CFLAGS) -o main main.o main.o: main.c $(CC) $(CFLAGS) -c main.c ``` ### 注意事项 - 如果选择修改源代码,请确保不会破坏程序逻辑。 - 如果选择调整编译器选项,请注意可能会影响其他警告的检测[^2]。
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