Create valid-number.cpp

Author: kamyu104

C++/valid-number.cpp

@@ -0,0 +1,64 @@
+// Time:  O(n)
+// Space: O(1)
+
+// automata: http://images.cnitblog.com/i/627993/201405/012016243309923.png
+class Solution {
+public:
+    bool isNumber(string s) {
+        enum InputType {
+            INVALID,    // 0
+            SPACE,      // 1
+            SIGN,       // 2
+            DIGIT,      // 3
+            DOT,        // 4
+            EXPONENT,   // 5
+            NUM_INPUTS  // 6
+        };
+        int transitionTable[][NUM_INPUTS] = {
+            -1,  0,  3,  1,  2, -1,     // next states for state 0
+            -1,  8, -1,  1,  4,  5,     // next states for state 1
+            -1, -1, -1,  4, -1, -1,     // next states for state 2
+            -1, -1, -1,  1,  2, -1,     // next states for state 3
+            -1,  8, -1,  4, -1,  5,     // next states for state 4
+            -1, -1,  6,  7, -1, -1,     // next states for state 5
+            -1, -1, -1,  7, -1, -1,     // next states for state 6
+            -1,  8, -1,  7, -1, -1,     // next states for state 7
+            -1,  8, -1, -1, -1, -1,     // next states for state 8
+        };
+
+        int state = 0;
+        for (const auto& c: s) {
+            InputType inputType = INVALID;
+            if (isspace(c)) {
+                inputType = SPACE;
+            } else if (c == '+' || c == '-') {
+                inputType = SIGN;
+            } else if (isdigit(c)) {
+                inputType = DIGIT;
+            } else if (c == '.') {
+                inputType = DOT;
+            } else if (c == 'e' || c == 'E') {
+                inputType = EXPONENT;
+            }
+            // Get next state from current state and input symbol
+            state = transitionTable[state][inputType];
+
+            // Invalid input
+            if (state == -1) {
+                return false;
+            }
+        }
+        // If the current state belongs to one of the accepting (final) states,
+        // then the number is valid
+        return state == 1 || state == 4 || state == 7 || state == 8;
+    }
+};
+
+#include <regex>
+class Solution_TLE {
+public:
+    bool isNumber(string s) {
+        regex e("^\\s*[\\+-]?((\\d+(\\.\\d*)?)|\\.\\d+)([eE][\\+-]?\\d+)?\\s*$");
+        return regex_match(s, e);
+    }
+};