add two solution

Author: freefcw

leetcode/decode-ways.go

@@ -0,0 +1,42 @@
+package leetcode
+
+// https://leetcode.com/problems/decode-ways/
+
+func isValidEncode(s string) bool {
+	if len(s) == 1 {
+		return s >= "1" && s <= "9"
+	}
+	if s <= "26" && s >= "10" {
+		return true
+	}
+	return false
+}
+
+func numDecodings(s string) int {
+	if len(s) == 0 {
+		return 0
+	}
+	dp := make([]int, len(s))
+	if isValidEncode(s[0:1]) {
+		dp[0] = 1
+	}
+	if len(s) == 1 {
+		return dp[0]
+	}
+	for i := 1; i < len(s); i++ {
+		total := 0
+		if isValidEncode(s[i : i+1]) {
+			total = dp[i-1]
+		}
+		if isValidEncode(s[i-1 : i+1]) {
+			if i == 1 {
+				total++
+			} else {
+				total = total + dp[i-2]
+			}
+		}
+		dp[i] = total
+	}
+
+	return dp[len(s)-1]
+}

leetcode/decode-ways_test.go

@@ -0,0 +1,42 @@
+package leetcode
+
+import "testing"
+
+func TestNumDecodings(t *testing.T) {
+	tests := []struct {
+		input  string
+		expect int
+	}{
+		{
+			input:  "12",
+			expect: 2,
+		}, {
+			input:  "22",
+			expect: 2,
+		}, {
+			input:  "226",
+			expect: 3,
+		}, {
+			input:  "0",
+			expect: 0,
+		}, {
+			input:  "010",
+			expect: 0,
+		}, {
+			input:  "0010",
+			expect: 0,
+		}, {
+			input:  "10",
+			expect: 1,
+		}, {
+			input:  "100",
+			expect: 0,
+		},
+	}
+	for i, item := range tests {
+		actual := numDecodings(item.input)
+		if actual != item.expect {
+			t.Fatalf("%d, expect %d, actual %d\n", i, item.expect, actual)
+		}
+	}
+}

leetcode/longest-palindromic-substring.go

@@ -0,0 +1,83 @@
+package leetcode
+
+// https://leetcode.com/problems/longest-palindromic-substring/
+
+func findPalindrome(s string, i int) int {
+	if s[i] == s[i-1] {
+		return i - 1
+	}
+	if i-2 >= 0 && s[i] == s[i-2] {
+		return i - 2
+	}
+	return -1
+}
+
+func isPalindrome(s string) bool {
+	if len(s) < 2 {
+		return false
+	}
+	i := 0
+	j := len(s) - 1
+	for i < j {
+		if s[i] != s[j] {
+			return false
+		}
+		i++
+		j--
+	}
+	return true
+}
+
+func longestPalindrome(s string) string {
+	if len(s) < 1 {
+		return ""
+	}
+	maxLen := 0
+	maxPos := 0
+	lens := make([]int, len(s))
+	lens[0] = -1
+	for i := 1; i < len(s); i++ {
+		lens[i] = -1
+		front := lens[i-1]
+		if front == -1 {
+			lens[i] = findPalindrome(s, i)
+			// fmt.Printf("0, %d %d\n", i, lens[i])
+		} else {
+			if front > 0 && s[i] == s[front-1] {
+				lens[i] = front - 1
+				for {
+					if lens[i] > 0 && lens[lens[i]] >= 0 {
+						if isPalindrome(s[lens[lens[i]] : i+1]) {
+							lens[i] = lens[lens[i]]
+						} else {
+							break
+						}
+					} else {
+						break
+					}
+				}
+			} else {
+				s2 := s[front : i+1]
+				// fmt.Printf("2, %d %d[%s]", front, i, s2)
+				if isPalindrome(s2) {
+					lens[i] = front
+				}
+			}
+		}
+		if lens[i] == -1 {
+			lens[i] = findPalindrome(s, i)
+		}
+		newLen := i - lens[i] + 1
+		if lens[i] > -1 && newLen > maxLen {
+			maxLen = newLen
+			maxPos = i
+		}
+		// fmt.Printf("i: %d, lens[i]:%d, maxLen: %d\n", i, lens[i], maxLen)
+	}
+
+	if maxLen == 0 {
+		return s[0:1]
+	}
+	// fmt.Printf("ret %d %d %v\n", maxPos, lens[maxPos], lens)
+	return s[lens[maxPos] : maxPos+1]
+}

leetcode/longest-palindromic-substring_test.go

@@ -0,0 +1,55 @@
+package leetcode
+
+import "testing"
+
+func TestLongestPalindrome(t *testing.T) {
+	tests := []struct {
+		input  string
+		expect string
+	}{
+		{
+			input:  "bananas",
+			expect: "anana",
+		}, {
+			input:  "babad",
+			expect: "bab",
+		}, {
+			input:  "ccc",
+			expect: "ccc",
+		}, {
+			input:  "cbbd",
+			expect: "bb",
+		}, {
+			input:  "abcdefg",
+			expect: "a",
+		}, {
+			input:  "bbbbbb",
+			expect: "bbbbbb",
+		}, {
+			input:  "abababac",
+			expect: "abababa",
+		}, {
+			input:  "abababab",
+			expect: "abababa",
+		}, {
+			input:  "aaaabbbbbb",
+			expect: "bbbbbb",
+		}, {
+			input:  "abcdcba",
+			expect: "abcdcba",
+		}, {
+			input:  "",
+			expect: "",
+		}, {
+			input:  "a",
+			expect: "a",
+		},
+	}
+
+	for i, item := range tests {
+		actual := longestPalindrome2(item.input)
+		if actual != item.expect {
+			t.Fatalf("%d expect %s, actual %s", i, item.expect, actual)
+		}
+	}
+}