leetcode -- Substring with Concatenation of All Words

 思路：

从左往右扫描主字符串，用两个map来统计字符串的出现次数

 这里L数组中可能会出现两个相同的字符串

import java.util.Collection;
public class Solution {
    public ArrayList<Integer> findSubstring(String S, String[] L) {
         ArrayList<Integer> results = new ArrayList<Integer>();
        int len = L.length;
        if (len == 0) {
            results.add(0);
            return results;
        }

        int M = S.length();
        int N = L[0].length();
        Map<String, Integer> expected = new HashMap<String, Integer>();
        Map<String, Integer> real = new HashMap<String, Integer>();
        for (int j = 0; j < len; j++) {
            if(expected.get(L[j]) == null){
                expected.put(L[j], 1);
                real.put(L[j], 0);
            } else{
                expected.put(L[j], expected.get(L[j]) + 1);
            }
        }

        for (int i = 0; i <= (M - N * len);) {
            int j = i;
            for (; j < i + N * len;) {
                String tmp = S.substring(j, j + N);
                if(expected.get(tmp) == null){
                    i = i + 1;
                    for (int m = 0; m < len; m++) {
                        real.put(L[m], 0);
                    }
                    break;
                }else {
                    real.put(tmp, real.get(tmp) + 1);
                    j = j + N;
                } 
            }

            if (j >= i + N * len) {
                boolean flag = true;
                for(int n = 0; n < L.length; n++){
                    if(expected.get(L[n]) != real.get(L[n])){
                        flag = false;
                        break;
                    }
                }
                
                if(flag){
                    results.add(i);
                    i = i + N;
                } else {
                    i = i + 1;
                }

                for (int m = 0; m < len; m++) {
                    real.put(L[m], 0);
                }
            }
        }
        return results;
    }
}

重构后代码：

public static ArrayList<Integer> findSubstring3(String S, String[] L) {
        ArrayList<Integer> results = new ArrayList<Integer>();
        int len = L.length;
        if (len == 0) {
            results.add(0);
            return results;
        }

        int M = S.length();
        int N = L[0].length();
        Map<String, Integer> expected = new HashMap<String, Integer>();
        Map<String, Integer> real = new HashMap<String, Integer>();
        for (int j = 0; j < len; j++) {
            if (expected.get(L[j]) == null) {
                expected.put(L[j], 1);
                real.put(L[j], 0);
            } else {
                expected.put(L[j], expected.get(L[j]) + 1);
            }
        }

        for (int i = 0; i <= (M - N * len); i++) {
            int j = 0;
            for (; j < len;) {
                String tmp = S.substring(i + j * N, i + (j + 1) * N);
                if (expected.get(tmp) == null) {
                    break;
                } else {
                    real.put(tmp, real.get(tmp) + 1);
                    if (real.get(tmp) > expected.get(tmp)) {
                        break;
                    }
                    j = j + 1;
                }
            }

            if (j == len) {
                results.add(i);
            }
            for (int m = 0; m < len; m++) {
                real.put(L[m], 0);
            }

        }
        return results;
    }

易错的几个数据集：

String S = "lingmindraboofooowingdingbarrwingmonkeypoundcake";
String[] L = new String[] { "fooo", "barr", "wing", "ding", "wing" };

String S2 = "aaa";
String[] L2 = new String[] { "a", "b" };

String S3 = "barfoothefoobarman";
String[] L3 = new String[] { "foo", "bar" };