字符串截取模板 && POJ 3450、3080 ( 暴力枚举子串 && KMP匹配 )

//截取字符串 ch 的 st~en 这一段子串返回子串的首地址
//注意用完需要根据需要最后free()掉

char* substring(char* ch,int st,int en)
{
    int length = en - st + 1;
    char* pch=ch;
    char* subch=(char*)malloc(length+1);
    pch=pch+st;
    for(int i=0;i<length;i++)   subch[i]=*(pch++);
    subch[length]=‘\0‘;
    return subch;
}

#include<string.h>
#include<stdio.h>
#include<string>
#include<malloc.h>
#include<stdlib.h>
using namespace std;
const int maxn = 60 + 5;
char str[10][maxn], fir[maxn];
char * mo, * ans;
int num, Next[maxn], moL;
char* substring(char* ch,int st,int en)
{
    int length = en - st + 1;
    char* pch=ch;
    char* subch=(char*)malloc(length+1);
    pch=pch+st;
    for(int i=0;i<length;i++)   subch[i]=*(pch++);
    subch[length]=‘\0‘;
    return subch;
}
inline void GetNext()
{
    int i = 0, j = -1;
    Next[i] = j;
    while(i < moL){
        while(j!=-1 && mo[i]!=mo[j]) j = Next[j];
        Next[++i] = ++j;
    }
}
bool KmpCount(int who)
{
    int i = 0, j = 0;
    while(j < moL && i < 60){
        while(j!=-1 && mo[j]!=str[who][i]) j = Next[j];
        i++, j++;
    }
    if(j == moL) return true;
    return false;
}
bool Is_Match(int st, int en)
{
    moL = en - st + 1;
    mo = substring(fir, st, en);
    GetNext();
    for(int k=1; k<num; k++){
        if(!KmpCount(k))
            return false;
    }return true;
}
inline void Find_better_ans(int pos, int len, int en)
{
    for(int i=pos+1; i<=en; i++){
        for(int k=0,j=i; j<=i+len; j++,k++){
            if(ans[k] > fir[j]){
                if(Is_Match(i, i+len)){
                    ans = substring(mo, 0, moL-1);
                }else { free(mo); break; }
            }else if(ans[k] < fir[j]) break;
        }
    }
}
bool Have_ans()
{
    for(int len=59; len>=1; len--){///枚举截取子串的长度，从大到小枚举
        for(int i=0; i<=59-len; i++){///在这个长度下，枚举所有子串的首字母
            if(Is_Match(i, i+len)){///判断是否匹配
                ans = substring(mo, 0, moL-1);
                Find_better_ans(i, len, 59-len);
                return true;
            }else free(mo);
        }
    }return false;
}
int main(void)
{
    int nCase;
    scanf("%d", &nCase);
    while(nCase--){
        scanf("%d", &num);
        scanf("%s", fir);
        for(int i=1; i<num; i++) scanf("%s", str[i]);
        if(Have_ans()) { puts(ans); free(ans); }
        else puts("no significant commonalities");
    }
    return 0;
}

#include<stdio.h>
#include<string.h>
#include<malloc.h>
#include<algorithm>
const int maxn = 4050;
char StrGroup[maxn][maxn], str[maxn], *mo, *ans;
int moL, Next[maxn], num, MinL, index, Len[maxn];
char* substring(int st,int en)
{
    int length = en - st + 1;
    char* subch=(char*)malloc(length+1);
    for(int i=0,j=st;i<length;j++,i++)   subch[i]=StrGroup[index][j];
    subch[length]=‘\0‘;
    return subch;
}
inline void GetNext()
{
    int i = 0, j = -1;
    Next[i] = j;
    while(i < moL){
        while(j!=-1 && mo[i]!=mo[j]) j = Next[j];
        Next[++i] = ++j;
    }
}
bool RunKmp(int who)
{
    int i = 0, j = 0;
    while(j < moL && i < Len[who]){
        while(j!=-1 && mo[j]!=StrGroup[who][i]) j = Next[j];
        i++, j++;
    }
    if(j == moL) return true;
    return false;
}
bool RunMatch()
{
    GetNext();
    for(int i=1; i<=num; i++){
        if(i!=index){
            if(!RunKmp(i)) return false;
        }
    }return true;
}

inline void Find_Better_Ans(int st, int len)
{
    for(int i=st+1; i<=MinL-len; i++){
        for(int j=i,k=0; k<len; j++,k++){
            //printf("ok %s\n", ans);
            if(ans[k] > StrGroup[index][j]){
                mo = substring(i, i+len-1);
                moL = strlen(mo);
                if(RunMatch()){
                    free(ans);
                    ans = mo;
                    break;
                }else{ free(mo); break; }
            }else if(ans[k] < StrGroup[index][j]) break;
        }
    }
}

bool Match(int len)
{
    for(int i=0; i<=MinL-len; i++){
        moL = len;
        mo = substring(i, i+len-1);
        if(RunMatch()){
            ans = mo;
            Find_Better_Ans(i, len);
            return true;
        }else free(mo);
    }return false;
}
inline void PrintAns()
{
    for(int len=MinL; len>0; len--)
        if(Match(len)){ puts(ans); free(ans); return; }
    puts("IDENTITY LOST");
}
int main(void)
{
    while(~scanf("%d", &num) && num){
        MinL = 0x3f3f3f3f;
        for(int i=1; i<=num; i++){
            scanf("%s", StrGroup[i]);
            Len[i] = strlen(StrGroup[i]);
            if(MinL > Len[i]){
                MinL = Len[i];
                index = i;
            }
        }PrintAns();
    }
    return 0;
}