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# 93. Restore IP Addresses

### Description

Given a string `s` containing only digits. Return all possible valid IP addresses that can be obtained from `s`. You can return them in **any** order.

A **valid IP address** consists of exactly four integers, each integer is between `0` and `255`, separated by single points and cannot have leading zeros. For example, "0.1.2.201" and "192.168.1.1" are **valid** IP addresses and "0.011.255.245", "192.168.1.312" and "192.168\@1.1" are **invalid** IP addresses. 

### Constraints

* `0 <= s.length <= 3000`
* `s` consists of digits only.

### Approach

### Links

* [GeeksforGeeks](https://www.geeksforgeeks.org/program-generate-possible-valid-ip-addresses-given-string/)
* [Leetcode](https://leetcode.com/problems/restore-ip-addresses/)
* [ProgramCreek](https://www.programcreek.com/2014/06/leetcode-restore-ip-addresses-java/)
* [YouTube](https://youtu.be/KU7Ae2513h0)

### **Examples**

{% tabs %}
{% tab title="Example 1" %}
**Input:** s = "25525511135"

**Output:** \["255.255.11.135", "255.255.111.35"]
{% endtab %}

{% tab title="Example 2" %}
**Input:** s = "0000"

**Output:** \["0.0.0.0"]
{% endtab %}

{% tab title="Example 3" %}
**Input:** s = "1111"

**Output:** \["1.1.1.1"]
{% endtab %}

{% tab title="Example 4" %}
**Input:** s = "010010"

**Output:** \["0.10.0.10", "0.100.1.0"]
{% endtab %}

{% tab title="Example 5" %}
**Input:** s = "101023"

**Output:** \["1.0.10.23", "1.0.102.3", "10.1.0.23", "10.10.2.3", "101.0.2.3"]
{% endtab %}
{% endtabs %}

### **Solutions**

{% tabs %}
{% tab title="Solution 1" %}

```java
/**
 * Time complexity : 
 * Space complexity : 
 */

class Solution {
    public List<String> restoreIpAddresses(String s) {
        List<String> resultList = new ArrayList<>();
        int n = s.length();
        if(n < 4 || n > 12) return resultList;
        for(int p = 1; p < 4; p++) {
            for(int q = 1; q < 4; q++) {
                for(int r = 1; r < 4; r++) {
                    for(int t = 1; t < 4; t++) {
                        if(p+q+r+t == n) {
                            int v1 = Integer.parseInt(s.substring(0, p));
                            if(v1 > 255) continue;
                            
                            int v2 = Integer.parseInt(s.substring(p, p+q));
                            if(v2 > 255) continue;
                            
                            int v3 = Integer.parseInt(s.substring(p+q, p+q+r));
                            if(v3 > 255) continue;
                            
                            int v4 = Integer.parseInt(s.substring(p+q+r));
                            if(v4 > 255) continue;
                            
                            String value = v1 + "." + v2 + "." + v3 + "." + v4;
                            if(value.length() == n+3) {
                                resultList.add(value);
                            }
                        }
                    }
                }
            }
        }
        return resultList;
    }
}
```

{% endtab %}
{% endtabs %}

### **Follow up**

*