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Commit34f6fd6

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update 162
1 parent2624c2d commit34f6fd6

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2 files changed

+76
-104
lines changed

2 files changed

+76
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lines changed
Lines changed: 39 additions & 74 deletions
Original file line numberDiff line numberDiff line change
@@ -1,84 +1,49 @@
11
packagecom.fishercoder.solutions;
22

3-
/**
4-
* 162. Find Peak Element
5-
6-
A peak element is an element that is greater than its neighbors.
7-
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Given an input array nums, where nums[i] ≠ nums[i+1], find a peak element and return its index.
9-
10-
The array may contain multiple peaks, in that case return the index to any one of the peaks is fine.
11-
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You may imagine that nums[-1] = nums[n] = -∞.
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Example 1:
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Input: nums = [1,2,3,1]
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Output: 2
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Explanation: 3 is a peak element and your function should return the index number 2.
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Example 2:
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Input: nums = [1,2,1,3,5,6,4]
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Output: 1 or 5
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Explanation: Your function can return either index number 1 where the peak element is 2,
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or index number 5 where the peak element is 6.
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Note:
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Your solution should be in logarithmic complexity.
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*/
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293
publicclass_162 {
304

31-
publicstaticclassSolution1 {
32-
/**
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* credit: https://discuss.leetcode.com/topic/29329/java-solution-and-explanation-using-invariants
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*
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* Basically, we need to keep this invariant:
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* nums[left] > nums[left-1], then we could return left as the result
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* or nums[right] > nums[right+1], then we could return right as the result
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*
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* Time: O(Ologn)
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*/
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publicintfindPeakElement(int[]nums) {
42-
if (nums ==null ||nums.length ==0) {
43-
return0;
44-
}
45-
intleft =0;
46-
intright =nums.length -1;
47-
while (left +1 <right) {
48-
intmid =left + (right -left) /2;
49-
if (nums[mid] <nums[mid +1]) {
50-
left =mid;
51-
}else {
52-
right =mid;
5+
publicstaticclassSolution1 {
6+
/**
7+
* credit: https://discuss.leetcode.com/topic/29329/java-solution-and-explanation-using-invariants
8+
* <p>
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* Basically, we need to keep this invariant:
10+
* nums[left] > nums[left-1], then we could return left as the result
11+
* or nums[right] > nums[right+1], then we could return right as the result
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* <p>
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* Time: O(logn)
14+
*/
15+
publicintfindPeakElement(int[]nums) {
16+
if (nums ==null ||nums.length ==0) {
17+
return0;
18+
}
19+
intleft =0;
20+
intright =nums.length -1;
21+
while (left +1 <right) {
22+
intmid =left + (right -left) /2;
23+
if (nums[mid] <nums[mid +1]) {
24+
left =mid;
25+
}else {
26+
right =mid;
27+
}
28+
}
29+
return (left ==nums.length -1 ||nums[left] >nums[left +1]) ?left :right;
5330
}
54-
}
55-
return (left ==nums.length -1 ||nums[left] >nums[left +1]) ?left :right;
5631
}
57-
}
5832

59-
publicstaticclassSolution2 {
60-
/**
61-
* My original O(n) solution.
62-
*/
63-
publicintfindPeakElement(int[]nums) {
64-
if (nums ==null ||nums.length ==0) {
65-
return0;
66-
}
67-
intn =nums.length;
68-
intresult =0;
69-
for (inti =0;i <n;i++) {
70-
if (i ==0 &&n >1 &&nums[i] >nums[i +1]) {
71-
result =i;
72-
break;
73-
}elseif (i ==n -1 &&i >0 &&nums[i] >nums[i -1]) {
74-
result =i;
75-
break;
76-
}elseif (i >0 &&i <n -1 &&nums[i] >nums[i -1] &&nums[i] >nums[i +1]) {
77-
result =i;
78-
break;
33+
publicstaticclassSolution2 {
34+
/**
35+
* My original O(n) solution.
36+
*/
37+
publicintfindPeakElement(int[]nums) {
38+
for (inti =1;i <nums.length;i++) {
39+
if (nums[i] >nums[i -1] &&i +1 <nums.length &&nums[i] >nums[i +1]) {
40+
returni;
41+
}
42+
if (i ==nums.length -1 &&nums[i] >nums[i -1]) {
43+
returni;
44+
}
45+
}
46+
return0;
7947
}
80-
}
81-
returnresult;
8248
}
83-
}
8449
}

‎src/test/java/com/fishercoder/_162Test.java

Lines changed: 37 additions & 30 deletions
Original file line numberDiff line numberDiff line change
@@ -7,34 +7,41 @@
77
importstaticorg.junit.Assert.assertEquals;
88

99
publicclass_162Test {
10-
privatestatic_162.Solution1solution1;
11-
privatestatic_162.Solution2solution2;
12-
privatestaticint[]nums;
13-
14-
@BeforeClass
15-
publicstaticvoidsetup() {
16-
solution1 =new_162.Solution1();
17-
solution2 =new_162.Solution2();
18-
}
19-
20-
@Test
21-
publicvoidtest1() {
22-
nums =newint[] {1,2};
23-
assertEquals(1,solution1.findPeakElement(nums));
24-
assertEquals(1,solution2.findPeakElement(nums));
25-
}
26-
27-
@Test
28-
publicvoidtest2() {
29-
nums =newint[] {1};
30-
assertEquals(0,solution1.findPeakElement(nums));
31-
assertEquals(0,solution2.findPeakElement(nums));
32-
}
33-
34-
@Test
35-
publicvoidtest3() {
36-
nums =newint[] {1,2,3,1};
37-
assertEquals(2,solution1.findPeakElement(nums));
38-
assertEquals(2,solution2.findPeakElement(nums));
39-
}
10+
privatestatic_162.Solution1solution1;
11+
privatestatic_162.Solution2solution2;
12+
privatestaticint[]nums;
13+
14+
@BeforeClass
15+
publicstaticvoidsetup() {
16+
solution1 =new_162.Solution1();
17+
solution2 =new_162.Solution2();
18+
}
19+
20+
@Test
21+
publicvoidtest1() {
22+
nums =newint[]{1,2};
23+
assertEquals(1,solution1.findPeakElement(nums));
24+
assertEquals(1,solution2.findPeakElement(nums));
25+
}
26+
27+
@Test
28+
publicvoidtest2() {
29+
nums =newint[]{1};
30+
assertEquals(0,solution1.findPeakElement(nums));
31+
assertEquals(0,solution2.findPeakElement(nums));
32+
}
33+
34+
@Test
35+
publicvoidtest3() {
36+
nums =newint[]{1,2,3,1};
37+
assertEquals(2,solution1.findPeakElement(nums));
38+
assertEquals(2,solution2.findPeakElement(nums));
39+
}
40+
41+
@Test
42+
publicvoidtest4() {
43+
nums =newint[]{1,2,1,3,5,6,4};
44+
assertEquals(5,solution1.findPeakElement(nums));
45+
assertEquals(1,solution2.findPeakElement(nums));
46+
}
4047
}

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