Add: Last Substring in Lexicographical Order

Author: openset

problems/last-substring-in-lexicographical-order/last_substring_in_lexicographical_order.go

@@ -0,0 +1,31 @@
+package problem_1163
+
+func lastSubstring(s string) string {
+	last, n := 0, len(s)
+	for i := 1; i < n; i++ {
+		if s[i-1] == s[i] {
+			// all of s[last:i+1] are the same letter.
+			// 'i' has no chance to be the new 'last'
+			// the reason is
+			// 1. s[i+1] > s[i], 'i+1' is the new 'last'
+			// 2. s[i+1] < s[i], 'last' is still 'last'
+			// 3. s[i+1] = s[i], 'i+1' is the new 'i'
+			// like above, need a different letter to make decision
+			continue
+		}
+		for l := 0; i+l < n; l++ {
+			if s[last+l] < s[i+l] {
+				// s[i:] is bigger than s[last:]
+				// new begin is here
+				last = i
+				break
+			}
+			if s[last+l] > s[i+l] {
+				// s[last:] is bigger than s[i:]
+				// no need to compare continue
+				break
+			}
+		}
+	}
+	return s[last:]
+}

problems/last-substring-in-lexicographical-order/last_substring_in_lexicographical_order_test.go

@@ -0,0 +1,35 @@
+package problem_1163
+
+import "testing"
+
+type caseType struct {
+	input    string
+	expected string
+}
+
+func TestLastSubstring(t *testing.T) {
+	tests := [...]caseType{
+		{
+			input:    "abab",
+			expected: "bab",
+		},
+		{
+			input:    "abcdabc",
+			expected: "dabc",
+		},
+		{
+			input:    "ffbcdfeda",
+			expected: "ffbcdfeda",
+		},
+		{
+			input:    "hksljkjsfjv",
+			expected: "v",
+		},
+	}
+	for _, tc := range tests {
+		output := lastSubstring(tc.input)
+		if output != tc.expected {
+			t.Fatalf("input: %v, output: %v, expected: %v", tc.input, output, tc.expected)
+		}
+	}
+}