.gitmodules

@@ -1,3 +1,11 @@
+[submodule "examples/diff/basic"]
+	path = examples/diff/basic
+	url = ssh://git@focs.ji.sjtu.edu.cn:2222/FOCS-dev/JOJ3-examples.git
+	branch = diff/basic
+[submodule "examples/diff/complex"]
+	path = examples/diff/complex
+	url = ssh://git@focs.ji.sjtu.edu.cn:2222/FOCS-dev/JOJ3-examples.git
+	branch = diff/complex
 [submodule "examples/cpplint/sillycode"]
 	path = examples/cpplint/sillycode
 	url = ssh://git@focs.ji.sjtu.edu.cn:2222/FOCS-dev/JOJ3-examples.git

examples/compile/error

@@ -1 +1 @@
-Subproject commit 2593e79505a93042d308c5fc355dba671dd4fdba
+Subproject commit 4e5fab93e5a0ce67c8f40fef1e8f4cab7018fc5d

examples/compile/success

@@ -1 +1 @@
-Subproject commit 638e9f661092d39daaf6e1ffc8ba5998fc56c96a
+Subproject commit 1512cb5f20473a598d7504a08dacff3d6406b983

examples/diff/basic

@@ -0,0 +1 @@
+Subproject commit af990327ab095c22a383448ad70d915f8d10490b

examples/diff/complex

@@ -0,0 +1 @@
+Subproject commit ac7a2fc912fb51af156cd4babb7e72148ebe1c14

internal/parsers/diff/parser.go

@@ -3,14 +3,29 @@ package diff
 import (
 	"fmt"
 	"os"
+	"strings"
+	"unicode"
 
 	"focs.ji.sjtu.edu.cn/git/FOCS-dev/JOJ3/internal/stage"
 )
 
+// operation represents the type of edit operation.
+type operation uint
+
+const (
+	INSERT operation = iota + 1
+	DELETE
+	MOVE
+)
+
 type Conf struct {
 	Cases []struct {
-		Score      int
+		Outputs []struct {
-		StdoutPath string
+			Score            int
+			FileName         string
+			AnswerPath       string
+			IgnoreWhitespace bool
+		}
 	}
 }
 
@@ -26,25 +41,195 @@ func (*Diff) Run(results []stage.ExecutorResult, confAny any) (
 	if len(conf.Cases) != len(results) {
 		return nil, true, fmt.Errorf("cases number not match")
 	}
+
 	var res []stage.ParserResult
 	for i, caseConf := range conf.Cases {
 		result := results[i]
 		score := 0
-		stdout, err := os.ReadFile(caseConf.StdoutPath)
+		comment := ""
-		if err != nil {
+		for _, output := range caseConf.Outputs {
-			return nil, true, err
+			answer, err := os.ReadFile(output.AnswerPath)
-		}
+			if err != nil {
-		// TODO: more compare strategies
+				return nil, true, err
-		if string(stdout) == result.Files["stdout"] {
+			}
-			score = caseConf.Score
+
+			// If no difference, assign score
+			if compareChars(string(answer), result.Files[output.FileName], output.IgnoreWhitespace) {
+				score += output.Score
+			} else {
+				// Convert answer to string and split by lines
+				stdoutLines := strings.Split(string(answer), "\n")
+				resultLines := strings.Split(result.Files[output.FileName], "\n")
+
+				// Generate Myers diff
+				diffOps := myersDiff(stdoutLines, resultLines)
+
+				// Generate diff block with surrounding context
+				diffOutput := generateDiffWithContext(stdoutLines, resultLines, diffOps)
+				comment += fmt.Sprintf(
+					"difference found in %s:\n```diff\n%s```\n",
+					output.FileName, diffOutput,
+				)
+			}
 		}
+
 		res = append(res, stage.ParserResult{
-			Score: score,
+			Score:   score,
-			Comment: fmt.Sprintf(
+			Comment: comment,
-				"executor status: run time: %d ns, memory: %d bytes",
-				result.RunTime, result.Memory,
-			),
 		})
 	}
+
 	return res, false, nil
 }
+
+// compareChars compares two strings character by character, optionally ignoring whitespace.
+func compareChars(stdout, result string, ignoreWhitespace bool) bool {
+	if ignoreWhitespace {
+		stdout = removeWhitespace(stdout)
+		result = removeWhitespace(result)
+	}
+	return stdout == result
+}
+
+// removeWhitespace removes all whitespace characters from the string.
+func removeWhitespace(s string) string {
+	var b strings.Builder
+	for _, r := range s {
+		if !unicode.IsSpace(r) {
+			b.WriteRune(r)
+		}
+	}
+	return b.String()
+}
+
+// myersDiff computes the Myers' diff between two slices of strings.
+// src: https://github.com/cj1128/myers-diff/blob/master/main.go
+func myersDiff(src, dst []string) []operation {
+	n := len(src)
+	m := len(dst)
+	max := n + m
+	var trace []map[int]int
+	var x, y int
+
+loop:
+	for d := 0; d <= max; d++ {
+		v := make(map[int]int, d+2)
+		trace = append(trace, v)
+
+		if d == 0 {
+			t := 0
+			for len(src) > t && len(dst) > t && src[t] == dst[t] {
+				t++
+			}
+			v[0] = t
+			if t == len(src) && len(src) == len(dst) {
+				break loop
+			}
+			continue
+		}
+
+		lastV := trace[d-1]
+
+		for k := -d; k <= d; k += 2 {
+			if k == -d || (k != d && lastV[k-1] < lastV[k+1]) {
+				x = lastV[k+1]
+			} else {
+				x = lastV[k-1] + 1
+			}
+
+			y = x - k
+
+			for x < n && y < m && src[x] == dst[y] {
+				x, y = x+1, y+1
+			}
+
+			v[k] = x
+
+			if x == n && y == m {
+				break loop
+			}
+		}
+	}
+
+	var script []operation
+	x = n
+	y = m
+	var k, prevK, prevX, prevY int
+
+	for d := len(trace) - 1; d > 0; d-- {
+		k = x - y
+		lastV := trace[d-1]
+
+		if k == -d || (k != d && lastV[k-1] < lastV[k+1]) {
+			prevK = k + 1
+		} else {
+			prevK = k - 1
+		}
+
+		prevX = lastV[prevK]
+		prevY = prevX - prevK
+
+		for x > prevX && y > prevY {
+			script = append(script, MOVE)
+			x -= 1
+			y -= 1
+		}
+
+		if x == prevX {
+			script = append(script, INSERT)
+		} else {
+			script = append(script, DELETE)
+		}
+
+		x, y = prevX, prevY
+	}
+
+	if trace[0][0] != 0 {
+		for i := 0; i < trace[0][0]; i++ {
+			script = append(script, MOVE)
+		}
+	}
+
+	return reverse(script)
+}
+
+// reverse reverses a slice of operations.
+func reverse(s []operation) []operation {
+	result := make([]operation, len(s))
+	for i, v := range s {
+		result[len(s)-1-i] = v
+	}
+	return result
+}
+
+// generateDiffWithContext creates a diff block with surrounding context from stdout and result.
+func generateDiffWithContext(stdoutLines, resultLines []string, ops []operation) string {
+	var diffBuilder strings.Builder
+
+	srcIndex, dstIndex := 0, 0
+
+	for _, op := range ops {
+		switch op {
+		case INSERT:
+			if dstIndex < len(resultLines) {
+				diffBuilder.WriteString(fmt.Sprintf("+ %s\n", resultLines[dstIndex]))
+				dstIndex++
+			}
+
+		case MOVE:
+			if srcIndex < len(stdoutLines) {
+				diffBuilder.WriteString(fmt.Sprintf("  %s\n", stdoutLines[srcIndex]))
+				srcIndex++
+				dstIndex++
+			}
+
+		case DELETE:
+			if srcIndex < len(stdoutLines) {
+				diffBuilder.WriteString(fmt.Sprintf("- %s\n", stdoutLines[srcIndex]))
+				srcIndex++
+			}
+		}
+	}
+
+	return diffBuilder.String()
+}