hdu 1358 & 1711 kmp 模板

怎麼說呢，之前看演算法的時候，覺得思想自己還是理解了，不過就這幾行代碼還真的太那個厲害了，其實現在最不明白的是init_next()函數

裡面的初始化i = 0; k = -1; _next[0] = -1;為什麼k 要初始化為-1？ 真的不懂，、……………………

#include<iostream>#define M 10000#define N 1000000using namespace std;int b[M];int a[N];int _next[N];int n,m;int kmp(){int i,j;i = 0;j = 0;while(i < n && j < m){if(j == -1 || a[i] ==  b[j]){i++;j++;}elsej = _next[j];}if(j == m)return i-m+1;return -1;}void init_next(){//非最佳化版int i,k;i = 0; k = -1; _next[0] = -1;while(i < m){if(k == -1 || b[i] == b[k]){i++;k++; _next[i] = k;}elsek = _next[k];}}void init_Next(){//最佳化版int i,k;i = 0; k = -1; _next[0] = -1;while(i < m){if(k == -1 || b[i] == b[k]){i++;k++;    if(b[i] != b[k])_next[i] = k;else_next[i] = _next[k];}elsek = _next[k];}}int main(){int tCase;cin >>tCase;while(tCase--){cin >>n >>m;for(int i = 0;i < n;i++){cin >>a[i];}for(int i = 0;i < m;i++){cin >>b[i];}init_Next();cout <<kmp() <<endl;}return 0;}