NC_142_MAX_DUPSUBSTR NC_149_KMP

package org.example.interview.practice;

/**
 * @author xianzhe.ma
 * @date 2021/11/7
 */

public class NC_142_MAX_DUPSUBSTR {

    public int solve (String a) {
        char[] aChar = a.toCharArray();
        int tabSize = aChar.length/2;
        //从最大窗口开始,比较两个窗口字符串数组
        for(;tabSize>0;tabSize--){
            //窗口可滑动次数为字符串数组长度减去(窗口长度*2),变化项为窗口左侧起始位置,每次滑动一格
            for(int tabSlide=0;tabSlide<=aChar.length-tabSize*2;tabSlide++){
                int compareSize = 0;
                //如果两个窗口对应字符串相同,直接返回长度
                if(compareTabString(aChar,tabSlide,tabSize)){
                    return tabSize*2;
                }
            }
        }
        //没有
        return 0;
    }
    //比较两个窗口字符串的函数(相同则返回true作为判断重复子串的标准)
    public boolean compareTabString(char[] a,int tabIndex,int tabSize){
        for(int i=tabIndex;i<tabIndex+tabSize;i++){
            if(a[i]!=a[i+tabSize])
                return false;
        }
        return true;
    }
}

package org.example.interview.practice;

/**
 * @author xianzhe.ma
 * @date 2021/7/27
 */

public class NC_149_KMP {

    public static int kmp (String mode, String mainString) {
        // write code here
        if (mode == null || mode.length() == 0 || mainString == null || mainString.length() == 0){
            return 0;
        }
        int[] next = getNext3(mode);
        int sIdx = 0;
        int tIdx = 0;
        int m = mode.length();
        int n = mainString.length();
        int count = 0;

        while(tIdx < n){
            if (sIdx == -1 || mode.charAt(sIdx) == mainString.charAt(tIdx)){
                tIdx ++;
                sIdx ++;
            }else{
                sIdx = next[sIdx];
            }
            if (sIdx == m){
//                count += 1;
//                sIdx = next[sIdx];
                //改写下 发现第一个返回下标
                return tIdx - m ;
            }
        }

        return count;
    }

    public static int kmp2 (String mode, String mainString) {
        // write code here
        if (mode == null || mode.length() == 0 || mainString == null || mainString.length() == 0){
            return 0;
        }
        int[] next = getNext3(mode);

        int lengM = mainString.length();
        int lengthS = mode.length();

        int mIndex = 0;//主
        int sIndex = 0;

        while (mIndex < lengM) {
            if (sIndex == -1 || mainString.charAt(mIndex) == mode.charAt(sIndex)) {
                sIndex++;
                mIndex++;
            } else {
                sIndex = next[sIndex];
            }

            if (sIndex == lengthS) {
                return mIndex - lengthS;
            }
        }

        return -1;
    }

    private static int[] getNext(String S){
        char[] chs = S.toCharArray();
        int n = chs.length;
        int[] nexts = new int[n + 1];
        nexts[0] = -1;
        nexts[1] = 0;
        int i = 2;
        int j = 0;

        while(i <= n) {
            if (j == -1 || chs[i - 1] == chs[j]){
                j++;
                nexts[i] = j;
                i++;
            }else{
                j = nexts[j];
            }
        }
        return nexts;
    }

    public static void main (String[] args) {
//        String s = "ababab";
//        String t = "abababab";

        String s = "ghxx";
        String t = "abbghxxrt";
        System.out.println(kmp(s,t));
    }

    public static int[] getNext2(String S) {
        char[] chs = S.toCharArray();

        int length = S.length();

        int[] next = new int[length + 1];

        int i = 2;
        int j = 0;
        next[0] = -1;
        next[1] = 0;
        while (i<=length) {
            if (j == -1 || chs[i-1] == chs[j]) {
                j++;
                next[i] = j;
                i++;
            } else {
                j = next[j];
            }

        }

        return next;

    }

    public static int[] getNext3(String str) {
        char[] chs = str.toCharArray();
        int length = str.length();

        int[] next = new int[length + 1];

        next[0] = -1;
        next[1] = 0;

        int i = 2;
        int j = -1;
        while (i<=length) {
            if (j == -1 || chs[i-1] == chs[j]) {
                j++;
                next[i] = j;
                i++;
            } else {
                j = next[j];
            }

        }

        return next;
    }
}