feat: 8_string_to_integer_atoi

8_string_to_integer_atoi/main.cpp

@@ -0,0 +1,75 @@
+#include <bits/stdc++.h>
+using namespace std;
+
+class Solution {
+   public:
+    void removeWhitespace(string &s) {
+        int i = 0;
+        while (i < s.length() && s[i] == ' ') i++;
+        s = s.substr(i);
+    }
+
+    void conversion(string &s) {
+        int i = 0;
+        while (i < s.length() && s[i] == '0') i++;
+        s = s.substr(i);
+
+        i = 0;
+        while (i < s.length() && s[i] >= '0' && s[i] <= '9') i++;
+        s = s.substr(0, i);
+    }
+
+    bool isLessThan(string a, string b) {
+        bool aIsNeg = false, bIsNeg = false;
+
+        if (a[0] == '-') {
+            aIsNeg = true;
+            a = a.substr(1);
+        }
+        if (b[0] == '-') {
+            bIsNeg = true;
+            b = b.substr(1);
+        }
+
+        bool aIsPos = !aIsNeg, bIsPos = !bIsNeg;
+
+        if (aIsNeg && bIsPos) return true;
+        if (aIsPos && bIsNeg) return false;
+
+        if (a.length() < b.length()) return aIsPos;
+        if (a.length() > b.length()) return aIsNeg;
+
+        for (int i = 0; i < a.length(); i++) {
+            if (a[i] < b[i]) return aIsPos;
+            if (a[i] > b[i]) return aIsNeg;
+        }
+
+        return false;
+    }
+
+    int myAtoi(string s) {
+        // step 1: ignore whitespace
+        removeWhitespace(s);
+        if (s.length() == 0) return 0;
+
+        // step 2: signedness
+        bool isNeg = false;
+        if (s[0] == '+') {
+            s = s.substr(1);
+        } else if (s[0] == '-') {
+            s = s.substr(1);
+            isNeg = true;
+        }
+        if (s.length() == 0) return 0;
+
+        // step 3: conversion
+        conversion(s);
+        if (s.length() == 0) return 0;
+
+        // step 4: rounding
+        if (isNeg) s.insert(s.begin(), '-');
+        if (isLessThan(s, to_string(INT32_MIN))) return INT32_MIN;
+        if (isLessThan(to_string(INT32_MAX), s)) return INT32_MAX;
+        return atoi(s.c_str());
+    }
+};