@@ -25,6 +25,8 @@ public SCC(int n) {
     }
 
     public void addEdge(int from, int to) {
+        rangeCheck(from);
+        rangeCheck(to);
         unorderedEdges.add(new Edge(from, to));
         start[from + 1]++;
         this.m++;
@@ -36,6 +38,7 @@ public int id(int i) {
                 "Graph hasn't been built."
             );
         }
+        rangeCheck(i);
         return ids[i];
     }
 
@@ -127,4 +130,12 @@ public int[][] build() {
         hasBuilt = true;
         return groups;
     }
+
+    private void rangeCheck(int i) {
+        if (i < 0 || i >= n) {
+            throw new IndexOutOfBoundsException(
+                String.format("Index %d out of bounds for length %d", i, n)
+            );
+        }
+    }
 }
Original file line number	Diff line number	Diff line change
`@@ -25,6 +25,8 @@ public SCC(int n) {`
`25`	`25`	`}`
`26`	`26`
`27`	`27`	`public void addEdge(int from, int to) {`
	`28`	`+ rangeCheck(from);`
	`29`	`+ rangeCheck(to);`
`28`	`30`	`unorderedEdges.add(new Edge(from, to));`
`29`	`31`	`start[from + 1]++;`
`30`	`32`	`this.m++;`
`@@ -36,6 +38,7 @@ public int id(int i) {`
`36`	`38`	`"Graph hasn't been built."`
`37`	`39`	`);`
`38`	`40`	`}`
	`41`	`+ rangeCheck(i);`
`39`	`42`	`return ids[i];`
`40`	`43`	`}`
`41`	`44`
`@@ -127,4 +130,12 @@ public int[][] build() {`
`127`	`130`	`hasBuilt = true;`
`128`	`131`	`return groups;`
`129`	`132`	`}`
	`133`	`+`
	`134`	`+ private void rangeCheck(int i) {`
	`135`	`+ if (i < 0 \|\| i >= n) {`
	`136`	`+ throw new IndexOutOfBoundsException(`
	`137`	`+ String.format("Index %d out of bounds for length %d", i, n)`
	`138`	`+ );`
	`139`	`+ }`
	`140`	`+ }`
`130`	`141`	`}`