3 problems

hitzzc · hitzzc · commit 4c1ca8d30c39 · 2016-10-16T10:20:09.000+08:00
diff --git a/README.md b/README.md
@@ -162,6 +162,9 @@ Golang solution for leetcode. For each problem, there is a simple *_test.go to t
 #### [201. Bitwise AND of Numbers Range](https://github.com/hitzzc/go-leetcode/tree/master/bitwise_AND_of_numbers_range)
 #### [202. Happy Number](https://github.com/hitzzc/go-leetcode/tree/master/happy_number)
 #### [203. Remove Linked List Elements](https://github.com/hitzzc/go-leetcode/tree/master/remove_linked_list_elements)
+#### [204. Count Primes](https://github.com/hitzzc/go-leetcode/tree/master/count_primes)
+#### [205. Isomorphic Strings](https://github.com/hitzzc/go-leetcode/tree/master/isomorphic_strings)
+#### [206. Reverse Linked List](https://github.com/hitzzc/go-leetcode/tree/master/reverse_linked_list)
 
 
 
diff --git a/count_primes/count_primes.go b/count_primes/count_primes.go
@@ -0,0 +1,22 @@
+package count_primes
+
+func countPrimes(n int) int {
+	check := make([]bool, n)
+	for i := 2; i*i < n; i++ {
+		if check[i] {
+			continue
+		}
+		for j := i; i*j < n; j++ {
+			if !check[i*j] {
+				check[i*j] = true
+			}
+		}
+	}
+	cnt := 0
+	for i := 2; i < n; i++ {
+		if !check[i] {
+			cnt++
+		}
+	}
+	return cnt
+}
diff --git a/isomorphic_strings/isomorphic_strings.go b/isomorphic_strings/isomorphic_strings.go
@@ -0,0 +1,24 @@
+package isomorphic_strings
+
+func isIsomorphic(s string, t string) bool {
+	if len(s) != len(t) {
+		return false
+	}
+	m := map[byte]byte{}
+	n := map[byte]byte{}
+	for i := range s {
+		if _, ok := m[t[i]]; !ok {
+			m[t[i]] = s[i]
+		}
+		if _, ok := n[s[i]]; !ok {
+			n[s[i]] = t[i]
+		}
+		if s[i] != m[t[i]] {
+			return false
+		}
+		if t[i] != n[s[i]] {
+			return false
+		}
+	}
+	return true
+}
diff --git a/reverse_linked_list/reverse_linked_list.go b/reverse_linked_list/reverse_linked_list.go
@@ -0,0 +1,20 @@
+package reverse_linked_list
+
+type ListNode struct {
+	Val  int
+	Next *ListNode
+}
+
+func reverseList(head *ListNode) *ListNode {
+	var tail, next *ListNode
+	for head != nil && head.Next != nil {
+		next = head.Next
+		head.Next = tail
+		tail = head
+		head = next
+	}
+	if head != nil {
+		head.Next = tail
+	}
+	return head
+}
