feat(): add atoi dart

Author: lambiengcode

README.md

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+## :lion: Leetcode
+
+### String to Int - Atoi
+
+```dart
+int myAtoi(String s) {
+  // Base condition
+  if (s.length < 1) {
+    return 0;
+  }
+  // MAX and MIN values for integers
+  final int max = 2147483647;
+  final int min = -2147483648;
+
+  s = s.trim();
+
+  // Counter
+  int i = 0;
+  // Flag to indicate if the number is negative
+  bool isNegative = s.startsWith("-");
+  // Flag to indicate if the number is positive
+  bool isPositive = s.startsWith("+");
+
+  if (isNegative) {
+    i++;
+  } else if (isPositive) {
+    i++;
+  }
+
+  // This will store the converted number
+  double number = 0;
+  // Loop for each numeric character in the sing iff numeric characters are leading
+  // characters in the sing
+  while (i < s.length &&
+      s[i].codeUnitAt(0) >= '0'.codeUnitAt(0) &&
+      s[i].codeUnitAt(0) <= '9'.codeUnitAt(0)) {
+    number = number * 10 + (s[i].codeUnitAt(0) - '0'.codeUnitAt(0));
+    i++;
+  }
+  // Give back the sign to the converted number
+  number = isNegative ? -number : number;
+  if (number < min) {
+    return min;
+  }
+  if (number > max) {
+    return max;
+  }
+  return number.round();
+}
+```

string_to_integer_atoi.dart

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+void main(List<String> args) {
+  List<String> cases = [
+    "42",
+    "   -42",
+    "+-2",
+    "4193 with words",
+    "-91283472332",
+    "00000-42a1234",
+    "words and 987",
+    "3.14159",
+  ];
+
+  for (final testcase in cases) {
+    print(myAtoi(testcase));
+  }
+}
+
+int myAtoi(String s) {
+  // Base condition
+  if (s.length < 1) {
+    return 0;
+  }
+  // MAX and MIN values for integers
+  final int max = 2147483647;
+  final int min = -2147483648;
+
+  s = s.trim();
+
+  // Counter
+  int i = 0;
+  // Flag to indicate if the number is negative
+  bool isNegative = s.startsWith("-");
+  // Flag to indicate if the number is positive
+  bool isPositive = s.startsWith("+");
+
+  if (isNegative) {
+    i++;
+  } else if (isPositive) {
+    i++;
+  }
+
+  // This will store the converted number
+  double number = 0;
+  // Loop for each numeric character in the sing iff numeric characters are leading
+  // characters in the sing
+  while (i < s.length &&
+      s[i].codeUnitAt(0) >= '0'.codeUnitAt(0) &&
+      s[i].codeUnitAt(0) <= '9'.codeUnitAt(0)) {
+    number = number * 10 + (s[i].codeUnitAt(0) - '0'.codeUnitAt(0));
+    i++;
+  }
+  // Give back the sign to the converted number
+  number = isNegative ? -number : number;
+  if (number < min) {
+    return min;
+  }
+  if (number > max) {
+    return max;
+  }
+  return number.round();
+}