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Commit2231165

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refactor 162
1 parenta79cb97 commit2231165

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2 files changed

+102
-50
lines changed

2 files changed

+102
-50
lines changed

‎src/main/java/com/fishercoder/solutions/_162.java

Lines changed: 62 additions & 50 deletions
Original file line numberDiff line numberDiff line change
@@ -2,71 +2,83 @@
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33
/**
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* 162. Find Peak Element
5-
*
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* A peak element is an element that is greater than its neighbors.
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Given an input array where num[i] ≠ num[i+1], find a peak element and return its index.
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A peak element is an element that is greater than its neighbors.
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Given an input array nums, where nums[i] ≠ nums[i+1], find a peak element and return its index.
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The array may contain multiple peaks, in that case return the index to any one of the peaks is fine.
9-
You may imagine that num[-1] = num[n] = -∞.
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For example, in array [1, 2, 3, 1], 3 is a peak element and your function should return the index number 2.*/
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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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1229
publicclass_162 {
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publicstaticclassSolution1 {
1432
/**
15-
* On discuss, this post has very good explanation about an O(logn) solution:
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* https://discuss.leetcode.com/topic/29329/java-solution-and-explanation-using-invariants
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*
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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:
1936
* nums[left] > nums[left-1], then we could return left as the result
2037
* 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)
2140
*/
22-
publicstaticintfindPeakElement_Ologn(int[]nums) {
23-
24-
if (nums ==null ||nums.length ==0) {
25-
return0;
26-
}
27-
intleft =0;
28-
intright =nums.length -1;
29-
while (left +1 <right) {
30-
intmid =left + (right -left) /2;
31-
if (nums[mid] <nums[mid +1]) {
32-
left =mid;
33-
}else {
34-
right =mid;
35-
}
41+
publicintfindPeakElement(int[]nums) {
42+
if (nums ==null ||nums.length ==0) {
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return0;
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}
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intleft =0;
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intright =nums.length -1;
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while (left +1 <right) {
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intmid =left + (right -left) /2;
49+
if (nums[mid] <nums[mid +1]) {
50+
left =mid;
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}else {
52+
right =mid;
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}
37-
return (left ==nums.length -1 ||nums[left] >nums[left +1]) ?left :right;
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}
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publicstaticvoidmain(String...strings) {
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// int[] nums = new int[]{1,2};
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// int[] nums = new int[]{1};
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int[]nums =newint[]{1,2,3,1};
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// System.out.println(findPeakElement(nums));
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System.out.println(findPeakElement_Ologn(nums));
54+
}
55+
return (left ==nums.length -1 ||nums[left] >nums[left +1]) ?left :right;
4756
}
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}
4858

59+
publicstaticclassSolution2 {
4960
/**
5061
* My original O(n) solution.
5162
*/
52-
publicstaticintfindPeakElement(int[]nums) {
53-
if (nums ==null ||nums.length ==0) {
54-
return0;
55-
}
56-
intn =nums.length;
57-
intresult =0;
58-
for (inti =0;i <n;i++) {
59-
if (i ==0 &&n >1 &&nums[i] >nums[i +1]) {
60-
result =i;
61-
break;
62-
}elseif (i ==n -1 &&i >0 &&nums[i] >nums[i -1]) {
63-
result =i;
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break;
65-
}elseif (i >0 &&i <n -1 &&nums[i] >nums[i -1] &&nums[i] >nums[i +1]) {
66-
result =i;
67-
break;
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}
63+
publicintfindPeakElement(int[]nums) {
64+
if (nums ==null ||nums.length ==0) {
65+
return0;
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}
67+
intn =nums.length;
68+
intresult =0;
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for (inti =0;i <n;i++) {
70+
if (i ==0 &&n >1 &&nums[i] >nums[i +1]) {
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result =i;
72+
break;
73+
}elseif (i ==n -1 &&i >0 &&nums[i] >nums[i -1]) {
74+
result =i;
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break;
76+
}elseif (i >0 &&i <n -1 &&nums[i] >nums[i -1] &&nums[i] >nums[i +1]) {
77+
result =i;
78+
break;
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}
70-
returnresult;
80+
}
81+
returnresult;
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}
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}
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}
Lines changed: 40 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,40 @@
1+
packagecom.fishercoder;
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importcom.fishercoder.solutions._162;
4+
importorg.junit.BeforeClass;
5+
importorg.junit.Test;
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7+
importstaticorg.junit.Assert.assertEquals;
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9+
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+
}
40+
}

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