几个经典算法研究

最近研究几个经典算法，比如二分查找，大数相加等。加强一下编码思路训练，这几个算法都不是很难，基本可以在演算中得到代码实现步骤，如下：

#include<stdio.h>
#include<string>
#include<vector>
#include <iostream>
using namespace std;
#define MAX 1010
const int NotFound = -1;

int Bsearch(const vector<string> &v, int start, int stop, string key) //二分查找，递归实现。当然之间用循环就可以了！
{
if (start > stop)
{
return NotFound;
}
int mid = (start + stop)/2;
if (key == v[mid])
{
return mid;
}
else if (key < v[mid])
{
return Bsearch(v, start, mid - 1, key);
}
else
{
return Bsearch(v, mid + 1, stop, key);
}
}
string bignumadd(const string str1, const string str2)  //大数相加
{
int a[MAX] = {0}, b[MAX] = {0};
int len1, len2, i, k, up = 0;
int len = 0;
char buf[512] = {0};
len1 = str1.length();
len2 = str2.length();
for(i = len1 - 1, k = 0; i >= 0; --i)
a[k++] = str1[i] - '0';
for(i = len2 - 1, k = 0; i >= 0; --i)
b[k++] = str2[i] - '0';
for(i = 0, up = 0; i < MAX; ++i)
{
a[i] = a[i] + b[i] + up;
up = a[i] / 10;
a[i] %= 10;
}
for(i = MAX -1; i >= 0; --i)
if(a[i]) break;
len += sprintf(buf + len, "%s + %s = ", str1.c_str(), str2.c_str());
for(k = i; k >= 0; --k)
{
len += sprintf(buf + len ,"%d", a[k]);
}
string str(buf);
printf("%s\n", buf);
return str;
}
void RecPermute(string sofar, string rest)  //全排列（递归算法）
{
if (rest == "")
{
cout << sofar << endl;
}
else
{
for (int i = 0; i < rest.length(); i++)
{
string next = sofar + rest.at(i);
string remaining = rest.substr(0, i)
+ rest.substr(i + 1, rest.length() - i);
RecPermute(next, remaining);
}
}
}
void move(int n,char src,char dest,char tmp) //汉诺塔问题
{
if(n==1)
printf("\t%c->%c\n",src,tmp);    //当n只有1个的时候直接从a移动到c
else
{
move(n-1,src,tmp,dest);            //第n-1个要从a通过c移动到b
printf("\t%c->%c\n",src,tmp);
move(n-1,dest,src,tmp);            //n-1个移动过来之后b变开始盘，b通过a移动到c，这边很难理解
}
}
int main()
{
RecPermute("","ABCD");

return 0;
}

******************************************************************************************************************

qsort排序函数在结构体数组中的运用

比如实现如下要求：

先按照学生姓名字典序排序，学生姓名一样的，按照分数从大到小排序。实例代码如下：

//============================================================================
// Name : CTest.cpp
// Author : @CodingGeek
// Version : 1.0
// Copyright : Your copyright notice
// Description : 几种常见的STL容器学习研究
//============================================================================
#include <iostream>
#include <string.h>
#include <stdlib.h>
using namespace std;

typedef struct
{
int id;
char name[20];
int score;
}T_Member;

T_Member g_MemIdTbl[] =
{
{1001, "zhangsan", 79},
{1004, "lisi", 78},
{1008, "wangwu", 85},
{1006, "zhaoliu", 87},
{1007, "sunqian", 67},
{1005, "wangyong", 78},
{1009, "caoxie", 76},
{1003, "wangwu", 90},
};

#define SIZE sizeof(g_MemIdTbl) / sizeof(g_MemIdTbl[0])

int compare_fun(const void *a, const void *b)
{
T_Member *pa = (T_Member*)a;
T_Member *pb = (T_Member*)b;

if (strcmp(pa->name,pb->name) != 0)
{
return strcmp(pa->name,pb->name);
}
else
{
return pb->score - pa->score;
}
}

int main()
{

qsort(g_MemIdTbl, SIZE, sizeof(g_MemIdTbl[0]),compare_fun);

for (unsigned i = 0; i < SIZE; i++)
{
cout << g_MemIdTbl[i].id<<":"<<g_MemIdTbl[i].name <<":"
<< g_MemIdTbl[i].score << endl;
}
return 0;
}