常见面试题学习（4）

1. 给出一个有N个数字（-1000..1000，N<=10^5）的环状序列，求一个和最大的连续子序列。

http://www.cppblog.com/baby-fly/archive/2010/08/04/122213.aspx?Pending=true 

来源于单调队列的应用

#include<iostream>
#include<queue>
using namespace std;
#define INF 0x3fffffff
#define maxn 100010
int num[maxn],sum[maxn];
int main()
{
    int T;
    int N,K,n;
    cin>>T;
    while(T--)
    {
        cin>>N>>K;
        sum[0]=0;
        for(int i=1;i<=N;i++)
        {
            cin>>num[i];
            sum[i]=sum[i-1]+num[i];
        }
        for(int i=N+1;i<N+K;i++)
        {
            sum[i]=sum[i-1]+num[i-N];
        }
        n=N+K-1;

        deque<int> q;
        q.clear();

        int ans=-INF;
        int start,end;
        //[j-kj] 枚举以j结尾的区间,找[j-k,j]中sum最小的i
        for(int j=1;j<=n;j++)
        {
            while(!q.empty() && sum[j-1]<sum[q.back()])
                q.pop_back();
            while(!q.empty() && q.front()<(j-K))
                q.pop_front();
            q.push_back(j-1);
            if(sum[j]-sum[q.front()]>ans)
            {
                ans=sum[j]-sum[q.front()];
                start=q.front()+1;
                end=j;
            }
        }
        cout<<ans<<" "<<start<<" "<<(end>N?end%N:end)<<endl;
    }
}

　　2. 一道微软的面试题

http://www.cnblogs.com/qsort/archive/2011/05/30/2063605.html 本着测试先行的原则 。。。 是啊，这得闲考虑多个情况后才编码

#include <stdio.h>
#include <assert.h>
#include <string.h>

// Test cases for leading & trailing spaces.
char arr00[] = "hello_world";
char arr01[] = "hello world";
char arr02[] = "  hello world";
char arr03[] = "hello world  ";
char arr04[] = "  hello world  ";
// Test cases for consecutive  spaces.
char arr05[] = "hello    world";
char arr06[] = "  hello    world  ";
// Test cases for spaces around new-lines.
char arr07[] = "hello  \n   world  ";
char arr08[] = "  hello    world   \n ";
char arr09[] = "\n  hello    world   \n ";
// Corner cases
char arr10[] = "   ";
char arr11[] = "\n";
char arr12[] = "  \n  ";

void filter_spaces(char *str, size_t len)
{
    char *dst   = str + len - 1;
    char *curr  = str + len - 1;

    while (*curr == ' ' && curr >= str)
        --curr; // remove trailing spaces;
    if (curr < str) { // all spaces.
        *str = '\0';
        return;
    }
    int after_space = 0;
    int around_newline = 0;
    while (curr >= str) {
        switch (*curr) {
        case ' ':
            if (after_space) { // a space followed by another space, omit it.
                --curr;
            } else if (around_newline) { // a space around a newline, omit it.
                --curr;
            } else {
                after_space = 1;
                *dst-- = *curr--;
            }
            break;
        case '\n':
            around_newline = 1;
            if (after_space) { // remove last recorded space.
                assert(*(dst + 1) == ' ');
                ++dst;
                after_space = 0;
            }
            *dst-- = *curr--;
            break;
        default: // other chars
            *dst-- = *curr--;
            after_space = 0;
            around_newline = 0;
            break;
        }
    }
    ++dst;
    if (*dst == ' ') // remove leading spaces.
        ++dst;
    // now the filtered string size is ( (str + size) - dst + 1 ),
    // including the trailing '\0'
    memmove(str, dst, (str + len) - dst + 1);

}

#define TEST_STR(str) do {\
    filter_spaces(str, strlen(str));\
    printf(#str ": \"%s\"\n", str);\
} while(0);

int main(int argc, char *argv[])
{
    TEST_STR(arr00);
    TEST_STR(arr01);
    TEST_STR(arr02);
    TEST_STR(arr03);
    TEST_STR(arr04);
    TEST_STR(arr05);
    TEST_STR(arr06);
    TEST_STR(arr07);
    TEST_STR(arr08);
    TEST_STR(arr09);
    TEST_STR(arr10);
    TEST_STR(arr11);
    TEST_STR(arr12);

    return 0;
}