KMP

 
#include <stdio.h>  
#include <iostream>  
#include <math.h>  
#include <string.h> 
#define d 1e-7  
using namespace std;  

int next[5],match[5005];
char text[5005];
char pattern[5]="NBA"; 
char take_place[5]="CBA"; 
inline void BuildNext(int length)
{
    int i, t;
    i = 1;
    t = 0;
    next[1] = 0;
    while(i < length + 1)
    {
        while(t > 0 && pattern[i - 1] != pattern[t - 1])
        {
            t = next[t];
        }
        ++t;
        ++i;
        if(pattern[i - 1] == pattern[t - 1])
        {
            next[i] = next[t];
        }
        else
        {
            next[i] = t;
        }
    }
    //pattern末尾的结束符控制，用于寻找目标字符串中的所有匹配结果用
    while(t > 0 && pattern[i - 1] != pattern[t - 1])
    {
        t = next[t];
    }
    ++t;
    ++i;
    next[i] = t;
}

int KMP(int text_length,int pattern_length)
{
    int i, j, n,k;
    BuildNext(pattern_length);
    i = 0;
    j = 1;
    n = 0;
    while(pattern_length+1-j<= text_length - i)
    {
        if(text[i] == pattern[j - 1])
        {
            ++i;
            ++j;

            //发现匹配结果，将匹配子串的位置，加入结果
            if(j == pattern_length + 1)
            {
                match[n++] = i - pattern_length;
                j = next[j];
            }
        }
        else
        {
            j = next[j];

            if(j == 0)
            {
                ++i;
                ++j;
            }
        }
    }
    return n;
}

int main()  
{  
    gest(text);
    int len_text = strlen(text);
    int len_pattern = strlen(pattern);
    int n = KMP(len_text,len_pattern);
    int i,j,k;
    //printf("%d\n",n);
//    for(i=0;i<n;i++)
    //    cout<<match[i]<<" ";
    //cout<<endl;
    for(i=0;i<n;i++)
    {
        k = 0;
        for(j=match[i];j<match[i]+3;j++,k++)
            text[j] = take_place[k];
    }
    printf("%s",text);
    return 0;
}