A non-empty array A consisting of N integers is given.
A peak is an array element which is larger than its neighbours. More precisely, it is an index P such that 0 < P < N − 1 and A[P − 1] < A[P] > A[P + 1].
For example, the following array A:
A[0] = 1 A[1] = 5 A[2] = 3 A[3] = 4 A[4] = 3 A[5] = 4 A[6] = 1 A[7] = 2 A[8] = 3 A[9] = 4 A[10] = 6 A[11] = 2has exactly four peaks: elements 1, 3, 5 and 10.
You are going on a trip to a range of mountains whose relative heights are represented by array A, as shown in a figure below. You have to choose how many flags you should take with you. The goal is to set the maximum number of flags on the peaks, according to certain rules.
Flags can only be set on peaks. What's more, if you take K flags, then the distance between any two flags should be greater than or equal to K. The distance between indices P and Q is the absolute value |P − Q|.
For example, given the mountain range represented by array A, above, with N = 12, if you take:
- two flags, you can set them on peaks 1 and 5;
- three flags, you can set them on peaks 1, 5 and 10;
- four flags, you can set only three flags, on peaks 1, 5 and 10.
You can therefore set a maximum of three flags in this case.
Write a function:
class Solution { public int solution(int[] A); }
that, given a non-empty array A of N integers, returns the maximum number of flags that can be set on the peaks of the array.
For example, the following array A:
A[0] = 1 A[1] = 5 A[2] = 3 A[3] = 4 A[4] = 3 A[5] = 4 A[6] = 1 A[7] = 2 A[8] = 3 A[9] = 4 A[10] = 6 A[11] = 2the function should return 3, as explained above.
Write an efficient algorithm for the following assumptions:
- N is an integer within the range [1..400,000];
- each element of array A is an integer within the range [0..1,000,000,000].
import java.util.ArrayList;
public int solution(int[] A) {
ArrayList<Integer> peakIndexes = new ArrayList<Integer>();
// find list of all the peaks
for (int i = 1; i < A.length - 1; i++) {
if (A[i - 1] < A[i] && A[i + 1] < A[i]) {
peakIndexes.add(i);
}
}
// any 2 peaks in the array must have a minimum distance of 2
if (peakIndexes.size() >= 2) {
return peakIndexes.size();
}
int minFlags = 1;
int maxFlags = peakIndexes.size();
int result = 3;
while (minFlags <= maxFlags) {
int flags = (minFlags + maxFlags) / 2;
boolean allFlagsUsed = false;
int flagsUsed = 0;
int indexThreshold = peakIndexes.get(0);
// plant flags
for (int peakIndex : peakIndexes) {
if (peakIndex >= indexThreshold) {
flagsUsed++;
indexThreshold = peakIndex + flags;
// all flags are now used
if (flagsUsed == flags) {
allFlagsUsed = true;
break;
}
}
}
// prepare for next round
if (allFlagsUsed) {
result = flags;
minFlags = flags + 1;
} else {
maxFlags = flags - 1;
}
}
return result;
}
Solution.java:2: class, interface, or enum expected public int solution(int[] A) { ^ Solution.java:5: class, interface, or enum expected for (int i = 1; i < A.length - 1; i++) { ^ Solution.java:5: class, interface, or enum expected for (int i = 1; i < A.length - 1; i++) { ^ Solution.java:5: class, interface, or enum expected for (int i = 1; i < A.length - 1; i++) { ^ Solution.java:8: class, interface, or enum expected } ^ Solution.java:14: class, interface, or enum expected } ^ Solution.java:18: class, interface, or enum expected int maxFlags = peakIndexes.size(); ^ Solution.java:19: class, interface, or enum expected int result = 3; ^ Solution.java:20: class, interface, or enum expected while (minFlags <= maxFlags) { ^ Solution.java:22: class, interface, or enum expected boolean allFlagsUsed = false; ^ Solution.java:23: class, interface, or enum expected int flagsUsed = 0; ^ Solution.java:24: class, interface, or enum expected int indexThreshold = peakIndexes.get(0); ^ Solution.java:27: class, interface, or enum expected for (int peakIndex : peakIndexes) { ^ Solution.java:30: class, interface, or enum expected indexThreshold = peakIndex + flags; ^ Solution.java:33: class, interface, or enum expected if (flagsUsed == flags) { ^ Solution.java:35: class, interface, or enum expected break; ^ Solution.java:36: class, interface, or enum expected } ^ Solution.java:43: class, interface, or enum expected minFlags = flags + 1; ^ Solution.java:44: class, interface, or enum expected } else { ^ Solution.java:46: class, interface, or enum expected } ^ Solution.java:49: class, interface, or enum expected }?????????? ^ 21 errors
import java.util.ArrayList;
class Solution {
public int solution(int[] A) {
ArrayList<Integer> peakIndexes = new ArrayList<Integer>();
// list all the peaks
for (int i = 1; i < A.length - 1; i++) {
if (A[i - 1] < A[i] && A[i + 1] < A[i]) {
peakIndexes.add(i);
}
}
// any 2 peaks in the array must have a minimum distance of 2
if (peakIndexes.size() >= 2) {
return peakIndexes.size();
}
int minFlags = 1;
int maxFlags = peakIndexes.size();
int result = 3;
while (minFlags <= maxFlags) {
int flags = (minFlags + maxFlags) / 2;
boolean allFlagsUsed = false;
int flagsUsed = 0;
int indexThreshold = peakIndexes.get(0);
// plant flags
for (int peakIndex : peakIndexes) {
if (peakIndex >= indexThreshold) {
flagsUsed++;
indexThreshold = peakIndex + flags;
// all flags are now used
if (flagsUsed == flags) {
allFlagsUsed = true;
break;
}
}
}
// prepare for next round
if (allFlagsUsed) {
result = flags;
minFlags = flags + 1;
} else {
maxFlags = flags - 1;
}
}
return result;
}
}
import java.util.ArrayList;
class Solution {
public int solution(int[] A) {
ArrayList<Integer> peakIndexes = new ArrayList<Integer>();
// list all the peaks
for (int i = 1; i < A.length - 1; i++) {
if (A[i - 1] < A[i] && A[i + 1] < A[i]) {
peakIndexes.add(i);
}
}
// any 2 peaks in the array must have a minimum distance of 2
if (peakIndexes.size() >= 2) {
return peakIndexes.size();
}
int minFlags = 1;
int maxFlags = peakIndexes.size();
int result = 3;
while (minFlags <= maxFlags) {
int flags = Math.round((minFlags + maxFlags) / 2.0f);
boolean allFlagsUsed = false;
int flagsUsed = 0;
int indexThreshold = peakIndexes.get(0);
// plant flags
for (int peakIndex : peakIndexes) {
if (peakIndex >= indexThreshold) {
flagsUsed++;
indexThreshold = peakIndex + flags;
// all flags are now used
if (flagsUsed == flags) {
allFlagsUsed = true;
break;
}
}
}
// prepare for next round
if (allFlagsUsed) {
result = flags;
minFlags = flags + 1;
} else {
maxFlags = flags - 1;
}
}
return result;
}
}
import java.util.ArrayList;
class Solution {
public int solution(int[] A) {
ArrayList<Integer> peakIndexes = new ArrayList<Integer>();
// list all the peaks
for (int i = 1; i < A.length - 1; i++) {
if (A[i - 1] < A[i] && A[i + 1] < A[i]) {
peakIndexes.add(i);
}
}
// any 2 peaks in the array must have a minimum distance of 2
if (peakIndexes.size() >= 2) {
return peakIndexes.size();
}
int minFlags = 1;
int maxFlags = peakIndexes.size();
int result = 1;
while (minFlags <= maxFlags) {
int flags = Math.round((minFlags + maxFlags) / 2.0f);
boolean allFlagsUsed = false;
int flagsUsed = 0;
int indexThreshold = peakIndexes.get(0);
// plant flags
for (int peakIndex : peakIndexes) {
if (peakIndex >= indexThreshold) {
flagsUsed++;
indexThreshold = peakIndex + flags;
// all flags are now used
if (flagsUsed == flags) {
allFlagsUsed = true;
break;
}
}
}
// prepare for next round
if (allFlagsUsed) {
result = flags;
minFlags = flags + 1;
} else {
maxFlags = flags - 1;
}
}
return result;
}
}
import java.util.ArrayList;
class Solution {
public int solution(int[] A) {
ArrayList<Integer> peakIndexes = new ArrayList<Integer>();
// list all the peaks
for (int i = 1; i < A.length - 1; i++) {
if (A[i - 1] < A[i] && A[i + 1] < A[i]) {
peakIndexes.add(i);
}
}
// any 2 peaks in the array must have a minimum distance of 2
if (peakIndexes.size() <= 2) {
return peakIndexes.size();
}
int minFlags = 1;
int maxFlags = peakIndexes.size();
int result = 1;
while (minFlags <= maxFlags) {
int flags = Math.round((minFlags + maxFlags) / 2.0f);
boolean allFlagsUsed = false;
int flagsUsed = 0;
int indexThreshold = peakIndexes.get(0);
// plant flags
for (int peakIndex : peakIndexes) {
if (peakIndex >= indexThreshold) {
flagsUsed++;
indexThreshold = peakIndex + flags;
// all flags are now used
if (flagsUsed == flags) {
allFlagsUsed = true;
break;
}
}
}
// prepare for next round
if (allFlagsUsed) {
result = flags;
minFlags = flags + 1;
} else {
maxFlags = flags - 1;
}
}
return result;
}
}
import java.util.ArrayList;
class Solution {
public int solution(int[] A) {
ArrayList<Integer> peakIndexes = new ArrayList<Integer>();
// list all the peaks
for (int i = 1; i < A.length - 1; i++) {
if (A[i - 1] < A[i] && A[i + 1] < A[i]) {
peakIndexes.add(i);
}
}
// any 2 peaks in the array must have a minimum distance of 2
if (peakIndexes.size() <= 2) {
return peakIndexes.size();
}
int minFlags = 1;
int maxFlags = peakIndexes.size();
int result = 3;
while (minFlags <= maxFlags) {
int flags = Math.round((minFlags + maxFlags) / 2.0f);
boolean allFlagsUsed = false;
int flagsUsed = 0;
int indexThreshold = peakIndexes.get(0);
// plant flags
for (int peakIndex : peakIndexes) {
if (peakIndex >= indexThreshold) {
flagsUsed++;
indexThreshold = peakIndex + flags;
// all flags are now used
if (flagsUsed == flags) {
allFlagsUsed = true;
break;
}
}
}
// prepare for next round
if (allFlagsUsed) {
result = flags;
minFlags = flags + 1;
} else {
maxFlags = flags - 1;
}
}
return result;
}
}
import java.util.ArrayList;
class Solution {
public int solution(int[] A) {
ArrayList<Integer> peakIndexes = new ArrayList<Integer>();
// list all the peaks
for (int i = 1; i < A.length - 1; i++) {
if (A[i - 1] < A[i] && A[i + 1] < A[i]) {
peakIndexes.add(i);
}
}
// any 2 peaks in the array must have a minimum distance of 2
if (peakIndexes.size() <= 2) {
return peakIndexes.size();
}
int minFlags = 1;
int maxFlags = peakIndexes.size();
int result = 3;
while (minFlags <= maxFlags) {
int flags = Math.round((minFlags + maxFlags) / 2.0f);
boolean allFlagsUsed = false;
int flagsUsed = 0;
int indexThreshold = peakIndexes.get(0);
// plant flags
for (int peakIndex : peakIndexes) {
if (peakIndex >= indexThreshold) {
flagsUsed++;
indexThreshold = peakIndex + flags;
// all flags are now used
if (flagsUsed == flags) {
allFlagsUsed = true;
break;
}
}
}
// prepare for next round
if (allFlagsUsed) {
result = flags;
minFlags = flags + 1;
} else {
maxFlags = flags - 1;
}
}
return result;
}
}
import java.util.ArrayList;
class Solution {
public int solution(int[] A) {
ArrayList<Integer> peakIndexes = new ArrayList<Integer>();
// list all the peaks
for (int i = 1; i < A.length - 1; i++) {
if (A[i - 1] < A[i] && A[i + 1] < A[i]) {
peakIndexes.add(i);
}
}
// any 2 peaks in the array must have a minimum distance of 2
if (peakIndexes.size() <= 2) {
return peakIndexes.size();
}
int minFlags = 1;
int maxFlags = peakIndexes.size();
int result = 3;
while (minFlags <= maxFlags) {
int flags = Math.round((minFlags + maxFlags) / 2.0f);
boolean allFlagsUsed = false;
int flagsUsed = 0;
int indexThreshold = peakIndexes.get(0);
// plant flags
for (int peakIndex : peakIndexes) {
if (peakIndex >= indexThreshold) {
flagsUsed++;
indexThreshold = peakIndex + flags;
// all flags are now used
if (flagsUsed == flags) {
allFlagsUsed = true;
break;
}
}
}
// prepare for next round
if (allFlagsUsed) {
result = flags;
minFlags = flags + 1;
} else {
maxFlags = flags - 1;
}
}
return result;
}
}
The solution obtained perfect score.