feat: solved 8

Author: fghpdf

src/com/fghpdf/StringToInteger/Solution.java

@@ -0,0 +1,75 @@
+package com.fghpdf.StringToInteger;
+
+/**
+ * @author fghpdf
+ * @date 2019/11/10
+ * https://leetcode.com/problems/string-to-integer-atoi/
+ *
+ * if else practice
+ **/
+public class Solution {
+	public int myAtoi(String str) {
+		str = str.trim();
+		if (str.length() == 0) {
+			return 0;
+		}
+		if (!isValid(str)) {
+			return 0;
+		}
+
+		int start = 0;
+		char sign = str.charAt(0);
+		if (sign == '+' || sign == '-') {
+			start = 1;
+		}
+
+		for (int i = start; i < str.length(); i++) {
+			char c = str.charAt(i);
+			if (!Character.isDigit(c)) {
+				str = str.substring(0, i);
+				break;
+			}
+		}
+
+		try {
+			return Integer.parseInt(str);
+		} catch (NumberFormatException error) {
+			if (sign == '+' || Character.isDigit(sign)) {
+				return 2147483647;
+			}
+
+			if (sign == '-') {
+				return -2147483648;
+			}
+		}
+
+		return 0;
+	}
+
+	private boolean isValid(String str) {
+		char c1 = str.charAt(0);
+
+		if (Character.isLetter(c1)) {
+			return false;
+		}
+
+		if (Character.isDigit(c1)) {
+			return true;
+		}
+
+		if ('+' == c1 || '-' == c1) {
+			if (str.length() < 2) {
+				return false;
+			}
+			char c2 = str.charAt(1);
+			return Character.isDigit(c2);
+		}
+
+		return false;
+	}
+
+	public static void main(String[] args) {
+		Solution sol = new Solution();
+		System.out.println(sol.myAtoi("20000000000000000000"));
+	}
+}