我试图使用递归找到所有可能增长最长的子序列。当我尝试输入数组{10,22,9,33,21,50,41,40,60,55}
时,它工作正常,输出为:
10 22 33 40 55 /
10 22 33 41 55 /
10 22 33 50 55 /
10 22 33 40 60 /
10 22 33 41 60 /
10 22 33 50 60 /
但是当我尝试输入数组{2,-3,4,90,-2,-1,-10,-9,-8}
时,我得到了一个输出:
-3 4 90 /
-3 -2 -1 /
-10 -9 -8 /
在这种情况下,我没有得到2 4 90
。我应该在代码中更改哪些内容以使其适用于此案例?
public class Main {
public static void main(String[] args) {
int arr[]={10,22,9,33,21,50,41,40,60,55};
int lis[]=new int[arr.length];
for(int i=0;i<arr.length;i++){
lis[i]=1;
}
for(int i=1;i<arr.length;i++){
for(int j=0;j<i;j++){
if(arr[i]>arr[j]&&lis[i]<lis[j]+1){
lis[i]=lis[j]+1;
}
}
}
int max=0;
for(int i=0;i<arr.length;i++){
if(max<lis[i])
max=lis[i];
}
//**************Recursive Print LIS****************
int rIndex=-1;
for(int i=arr.length-1;i>=0;i--){
if(lis[i]==max){
rIndex=i;
break;
}
}
int res[]=new int[max];
printLISRecursive(arr,rIndex,lis,res,max,max);
}
private static void printLISRecursive(int[] arr, int maxIndex, int[] lis, int[] res, int i, int max) {
if(maxIndex<0)return;
if(max==1&&lis[maxIndex]==1&&i==1){
res[i-1]=arr[maxIndex];
// System.out.println("Using Print Recursion:");
for(int j=0;j<res.length;j++){
System.out.print(res[j]+" ");
}
System.out.println();
return;
}
if(lis[maxIndex]==max){
res[i-1]=arr[maxIndex];
printLISRecursive(arr, maxIndex-1, lis, res, i-1, max-1);
}
printLISRecursive(arr, maxIndex-1, lis, res, i, max);
}
}
答案 0 :(得分:2)
public static String lcs(String a, String b){
int aLen = a.length();
int bLen = b.length();
if(aLen == 0 || bLen == 0){
return "";
}else if(a.charAt(aLen-1) == b.charAt(bLen-1)){
return lcs(a.substring(0,aLen-1),b.substring(0,bLen-1))
+ a.charAt(aLen-1);
}else{
String x = lcs(a, b.substring(0,bLen-1));
String y = lcs(a.substring(0,aLen-1), b);
return (x.length() > y.length()) ? x : y;
}
}
答案 1 :(得分:1)
public static int lcsrec(String x, String y) {
// If one of the strings has one character, search for that character
// in the other string and return the appropriate answer.
if (x.length() == 1)
return find(x.charAt(0), y);
if (y.length() == 1)
return find(y.charAt(0), x);
// Solve the problem recursively.
// Corresponding beginning characters match.
if (x.charAt(0) == y.charAt(0))
return 1+lcsrec(x.substring(1), y.substring(1));
// Corresponding characters do not match.
else
return max(lcsrec(x,y.substring(1)), lcsrec(x.substring(1),y));
}
答案 2 :(得分:0)
根据您的回溯想法,我编写以下代码。为简单起见,可以删除许多输入参数。
public class LIS {
private static int[] count;
public int longestIncreaseSubsequence(int[] seq) {
int n = seq.length;
for (int i = 0; i < n; i++) {
count[i] = 1;
}
for (int i = 1; i < n; i++) {
int max = 0;
for (int j = i-1; j >= 0; j--) {
if (seq[j] < seq[i]) max = Math.max(max, count[j]);
}
count[i] = max + 1;
}
int max = Integer.MIN_VALUE;
for (int i = 0; i < count.length; i++) {
if (count[i] > max) max = count[i];
}
return max;
}
public void printLIS(int[] a, int k, int[] count, int[] arr, int max) {
if (k == max) {
for (int i = max; i >= 1; i--) {
System.out.printf("%d ", arr[a[i]]);
}
System.out.println();
} else {
k++;
int[] candidates = new int[arr.length];
int ncandidate = 0;
for (int i = a[k-1]; i >= 0; i--) {
if (count[i] == max-k+1 && (arr[i] < arr[a[k-1]] || count[i] == max)) {
candidates[ncandidate] = i;
ncandidate++;
}
}
for (int i = 0; i < ncandidate; i++) {
a[k] = candidates[i];
printLIS(a, k, count, arr, max);
}
}
}
public static void main(String[] args) {
int[] input = {2,-3,4,90,-2,-1,-10,-9,-8};
LIS lis = new LIS();
count = new int[input.length];
int max = lis.longestIncreaseSubsequence(input);
int[] a = new int[max+1];
a[0] = input.length-1;
lis.printLIS(a, 0, count, input, max);
}
}