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dingjikerbo · dingjikerbo · commit 7419e850880d · 2018-11-22T12:09:06.000+08:00
diff --git a/leetcode/solution/src/LongestSubstringWithAtMostTwoDistinctCharacters.java b/leetcode/solution/src/LongestSubstringWithAtMostTwoDistinctCharacters.java
@@ -1,24 +1,22 @@
 public class LongestSubstringWithAtMostTwoDistinctCharacters {
 
-    // 7ms
+    // 1ms
     public int lengthOfLongestSubstringTwoDistinct2(String s) {
-        int[] count = new int[256];
-        int distinct = 0, longest = 0;
-
+        if (s.length() == 0) {
+            return 0;
+        }
+        int[] dp = new int[256];
+        int count = 0, longest = 0;
         for (int i = 0, j = 0; j < s.length(); j++) {
-            if (count[s.charAt(j)]++ == 0) {
-                distinct++;
-            }
-
-            for ( ; i < j && distinct > 2; ) {
-                if (--count[s.charAt(i++)] == 0) {
-                    --distinct;
+            if (dp[s.charAt(j)]++ == 0) {
+                for (++count; i <= j && count > 2; ) {
+                    if (--dp[s.charAt(i++)] == 0) {
+                        --count;
+                    }
                 }
             }
-
             longest = Math.max(longest, j - i + 1);
         }
-
         return longest;
     }
 }
diff --git a/leetcode/solution/src/String2Integer.java b/leetcode/solution/src/String2Integer.java
@@ -13,40 +13,35 @@
 public class String2Integer {
 
     public int myAtoi(String str) {
-        long n = 0;
-
-        str = str.trim();
-
-        // 这里要防御空串
-        if (str.length() == 0) {
-            return 0;
-        }
-
-        int sign = 1;
-
-        switch (str.charAt(0)) {
-            case '-':
+        int i = 0, sign = 1;
+        for ( ; i < str.length() && str.charAt(i) == ' '; i++);
+        if (i < str.length()) {
+            char csign = str.charAt(i);
+            if (csign == '-') {
                 sign = -1;
-            case '+':
-                str = str.substring(1);
-                break;
+                i++;
+            } else if (csign == '+') {
+                sign = 1;
+                i++;
+            } else if (csign < '0' || csign > '9') {
+                return 0;
+            } else {}
         }
-
-        for (char c : str.toCharArray()) {
-            if (c >= '0' && c <= '9') {
-                n = n * 10 + (c - '0');
-
-                if (n * sign > Integer.MAX_VALUE) {
-                    return Integer.MAX_VALUE;
-                } else if (n * sign < Integer.MIN_VALUE) {
-                    return Integer.MIN_VALUE;
-                }
-
-            } else {
+        long number = 0;
+        for ( ; i < str.length(); i++) {
+            char c = str.charAt(i);
+            if (c < '0' || c > '9') {
                 break;
             }
-        }
+            number = number * 10 + (c - '0');
 
-        return (int) (n * sign);
+            if (number * sign > Integer.MAX_VALUE) {
+                return Integer.MAX_VALUE;
+            }
+            if (number * sign < Integer.MIN_VALUE) {
+                return Integer.MIN_VALUE;
+            }
+        }
+        return (int) (number * sign);
     }
 }
diff --git a/leetcode/src/Main.java b/leetcode/src/Main.java
@@ -2,25 +2,40 @@
 
 public class Main {
 
-    public static int coinChange(int[] coins, int amount) {
-        Arrays.sort(coins);
-        int[] dp = new int[amount + 1];
-        Arrays.fill(dp, -1);
-        dp[0] = 0;
-        for (int i = 1; i <= amount; i++) {
-            for (int coin: coins) {
-                if (i - coin >= 0 && dp[i - coin] >= 0) {
-                    int k = dp[i - coin] + 1;
-                    dp[i] = dp[i] > 0 ? Math.min(dp[i], k) : k;
-                }
+    public static int myAtoi(String str) {
+        int i = 0, sign = 1;
+        for ( ; i < str.length() && str.charAt(i) == ' '; i++);
+        if (i < str.length()) {
+            char csign = str.charAt(i);
+            if (csign == '-') {
+                sign = -1;
+                i++;
+            } else if (csign == '+') {
+                sign = 1;
+                i++;
+            } else if (csign < '0' || csign > '9') {
+                return 0;
+            } else {}
+        }
+        long number = 0;
+        for ( ; i < str.length(); i++) {
+            char c = str.charAt(i);
+            if (c < '0' || c > '9') {
+                break;
+            }
+            number = number * 10 + (c - '0');
+
+            if (number * sign > Integer.MAX_VALUE) {
+                return Integer.MAX_VALUE;
+            }
+            if (number * sign < Integer.MIN_VALUE) {
+                return Integer.MIN_VALUE;
             }
         }
-        return dp[amount];
+        return (int) (number * sign);
     }
 
     public static void main(String[] args) {
-        System.out.println(coinChange(new int[] {
-                1, 2, 5
-        }, 11));
+        System.out.println(myAtoi("-42"));
     }
 }
