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RestoreIpAddresses.java
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RestoreIpAddresses.java
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package Algorithms.string;
import java.util.ArrayList;
import java.util.List;
public class RestoreIpAddresses {
public static void main(String[] strs) {
System.out.println(restoreIpAddresses("0000"));
}
public List<String> restoreIpAddresses1(String s) {
if (s == null) {
return null;
}
ArrayList<String> ret = new ArrayList<String>();
ArrayList<String> path = new ArrayList<String>();
dfs(s, 0, path, ret);
return ret;
}
public void dfs(String s, int index, ArrayList<String> path, ArrayList<String> ret) {
if (path.size() == 4) {
if (index == s.length()) {
StringBuilder sb = new StringBuilder();
for (String str: path) {
sb.append(str);
sb.append('.');
}
sb.deleteCharAt(sb.length() - 1);
ret.add(sb.toString());
}
return;
}
int len = s.length();
for (int i = index; i < index + 3 && i < len; i++) {
if (s.charAt(index) == '0' && i > index) {
break;
}
String pre = s.substring(index, i + 1);
int num = Integer.parseInt(pre);
if (num > 255) {
continue;
}
path.add(pre);
dfs(s, i + 1, path, ret);
path.remove(path.size() - 1);
}
}
// 2015.1.1 Redo:
public List<String> restoreIpAddresses2(String s) {
List<String> ret = new ArrayList<String>();
// Bug 1: not length, but length().
if (s == null || s.length() < 4 || s.length() > 12) {
return ret;
}
dfs(s, new ArrayList<String>(), ret, 0);
return ret;
}
public void dfs(String s, List<String> path, List<String> ret, int index) {
// THE BASE CASE:
int len = s.length();
if (path.size() == 4) {
// Create a solution.
if (index == len) {
StringBuilder sb = new StringBuilder();
for (String str: path) {
sb.append(str);
sb.append(".");
}
sb.deleteCharAt(sb.length() - 1);
// bug 3: forget this statement.
ret.add(sb.toString());
}
return;
}
// 2/ 25 / 255
// bug 2: i should < len.
for (int i = index; i < index + 3 && i < len; i++) {
String sub = s.substring(index, i + 1);
if (s.charAt(index) == '0' && i != index) {
// only allow 0, not 02, 022
break;
}
if (!isValid(sub)) {
continue;
}
path.add(sub);
dfs(s, path, ret, i + 1);
path.remove(path.size() - 1);
}
}
// 2015.1.20.
public boolean isValid1(String s) {
int num = Integer.parseInt(s);
return num >= 0 && num <= 255;
}
public static List<String> restoreIpAddresses(String s) {
// 1850
List<String> ret = new ArrayList<String>();
if (s == null) {
return ret;
}
dfs(s, 0, new ArrayList<String>(), ret);
return ret;
}
public static void dfs(String s, int index, List<String> path, List<String> ret) {
int len = s.length();
if (index == len && path.size() == 4) {
StringBuilder sb = new StringBuilder();
for (String str: path) {
sb.append(str + ".");
}
sb.deleteCharAt(sb.length() - 1);
ret.add(sb.toString());
return;
} else if (index == len || path.size() == 4) {
// base case. out of range.
return;
}
// bug 2: should use i < len to avoid overflow.
for (int i = index; i < index + 3 && i < len; i++) {
// Bug 1: Line 29: error: cannot find symbol: method sub(int,int)
String sub = s.substring(index, i + 1);
if (!isValid(sub)) {
continue;
}
path.add(sub);
dfs(s, i + 1, path, ret);
path.remove(path.size() - 1);
}
}
public static boolean isValid(String s) {
if (s.length() != 1 && s.charAt(0) == '0') {
return false;
}
int num = Integer.parseInt(s);
return num <= 255 && num >= 0;
}
}