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Commita1fada8

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add a solution for 395
1 parentcff8014 commita1fada8

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2 files changed

+101
-5
lines changed

2 files changed

+101
-5
lines changed

‎src/main/java/com/fishercoder/solutions/_395.java

Lines changed: 59 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -37,4 +37,63 @@ int findLongestSubstring(char[] chars, int start, int end, int k) {
3737
returnend -start;
3838
}
3939
}
40+
41+
publicstaticclassSolution2 {
42+
/**
43+
* classic sliding window approach.
44+
* credit: https://leetcode.com/problems/longest-substring-with-at-least-k-repeating-characters/discuss/170010/Java-O(n)-Solution-with-Detailed-Explanation-Sliding-Window/774350
45+
*/
46+
publicintlongestSubstring(Strings,intk) {
47+
intres =0;
48+
for (intnumUniqueTarget =1;numUniqueTarget <=26;numUniqueTarget++) {
49+
res =Math.max(res,slidingWindowHelper(s,k,numUniqueTarget));
50+
}
51+
returnres;
52+
}
53+
54+
// sliding window template
55+
privateintslidingWindowHelper(Strings,intk,intnumUniqueTarget) {
56+
int[]map =newint[26];
57+
intstart =0;
58+
intend =0;
59+
intres =0;
60+
intuniqueLetterCount =0;
61+
intnumNoLessThanK =0;
62+
while (end <s.length()) {
63+
charc1 =s.charAt(end);
64+
if (map[c1 -'a'] ==0) {
65+
//we increment this when we include a new letter into our sliding window
66+
uniqueLetterCount++;
67+
}
68+
map[c1 -'a']++;
69+
if (map[c1 -'a'] ==k) {
70+
//we increment this number when we find a letter's frequency reaches k
71+
numNoLessThanK++;
72+
}
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end++;
74+
75+
while (uniqueLetterCount >numUniqueTarget) {
76+
//as long as the counter (the number of qualified letters) is greater than our target number,
77+
//we can move the left pointer to the right,
78+
//this keeps the interval within our sliding window always valid
79+
charc2 =s.charAt(start);
80+
if (map[c2 -'a'] ==k) {
81+
//we decrement this numNoLessThanK when we find this letter's frequency equals
82+
//to k because we'll move past this letter, i.e. our sliding window no longer includes it
83+
numNoLessThanK--;
84+
}
85+
map[c2 -'a']--;
86+
if (map[c2 -'a'] ==0) {
87+
uniqueLetterCount--;
88+
}
89+
start++;
90+
}
91+
92+
if (uniqueLetterCount ==numNoLessThanK) {
93+
res =Math.max(res,end -start);
94+
}
95+
}
96+
returnres;
97+
}
98+
}
4099
}

‎src/test/java/com/fishercoder/_395Test.java

Lines changed: 42 additions & 5 deletions
Original file line numberDiff line numberDiff line change
@@ -6,26 +6,63 @@
66

77
importstaticjunit.framework.Assert.assertEquals;
88

9-
/**
10-
* Created by fishercoder on 12/31/16.
11-
*/
129
publicclass_395Test {
1310

1411
privatestatic_395.Solution1solution1;
12+
privatestatic_395.Solution2solution2;
13+
privatestaticStrings;
14+
privatestaticintk;
15+
privatestaticintexpected;
1516

1617
@BeforeClass
1718
publicstaticvoidsetup() {
1819
solution1 =new_395.Solution1();
20+
solution2 =new_395.Solution2();
1921
}
2022

2123
@Test
2224
publicvoidtest1() {
23-
assertEquals(5,solution1.longestSubstring("ababbc",2));
25+
s ="ababbc";
26+
expected =5;
27+
k =2;
28+
assertEquals(expected,solution1.longestSubstring(s,k));
29+
assertEquals(expected,solution2.longestSubstring(s,k));
2430
}
2531

2632
@Test
2733
publicvoidtest2() {
28-
assertEquals(3,solution1.longestSubstring("aaabb",3));
34+
s ="aaabb";
35+
k =3;
36+
expected =3;
37+
assertEquals(expected,solution1.longestSubstring(s,k));
38+
assertEquals(expected,solution2.longestSubstring(s,k));
39+
}
40+
41+
@Test
42+
publicvoidtest3() {
43+
s ="bbaaacbd";
44+
k =3;
45+
expected =3;
46+
assertEquals(expected,solution1.longestSubstring(s,k));
47+
assertEquals(expected,solution2.longestSubstring(s,k));
48+
}
49+
50+
@Test
51+
publicvoidtest4() {
52+
s ="weitong";
53+
k =2;
54+
expected =0;
55+
assertEquals(expected,solution1.longestSubstring(s,k));
56+
assertEquals(expected,solution2.longestSubstring(s,k));
57+
}
58+
59+
@Test
60+
publicvoidtest5() {
61+
s ="a";
62+
k =2;
63+
expected =0;
64+
assertEquals(expected,solution1.longestSubstring(s,k));
65+
assertEquals(expected,solution2.longestSubstring(s,k));
2966
}
3067

3168
}

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