93.Restore IP Addresses

Author: ZQKC

93.Restore IP Addresses.cpp

@@ -0,0 +1,32 @@
+class Solution {
+private:
+    void dfs(const std::string &s, int beg, std::string ip, int num, std::vector<std::string> &ans) {
+        if (beg == s.length() && num == 4) {
+            ans.push_back(ip);
+        }
+        if (s.length() - beg > (4 - num) * 3) {
+            return ;
+        }
+
+        std::string tmp_ip;
+        for (int i = 0, val = 0; i < 3; ++i) {
+            val *= 10;
+            val += (s[beg + i] - '0');
+            tmp_ip += s[beg + i];
+            if (val > 255 || (val != 0 && tmp_ip[0] == '0') || (val == 0 && tmp_ip.length() > 1)) {
+                continue;
+            }
+            if (num == 0)
+                dfs(s, beg + i + 1, tmp_ip, num + 1, ans);
+            else
+                dfs(s, beg + i + 1, ip + '.' + tmp_ip, num + 1, ans);
+        }
+    }
+
+public:
+    vector<string> restoreIpAddresses(string s) {
+        std::vector<std::string> ans;
+        dfs(s, 0, "", 0, ans);
+        return ans;
+    }
+};