Create 2097-valid-arrangement-of-pairs.js

Author: everthis

2097-valid-arrangement-of-pairs.js

@@ -0,0 +1,36 @@
+const packDGInOutDegreeMap = (gm, edges, dm) => { for (const [u, v] of edges) { if (!gm.has(u)) gm.set(u, []); gm.get(u).push(v); dm.set(u, (dm.get(u) || 0) + 1); dm.set(v, (dm.get(v) || 0) - 1); } };
+
+/**
+ * @param {number[][]} pairs
+ * @return {number[][]}
+ */
+const validArrangement = (pairs) => {
+    let g = new Map(), deg = new Map(), res = [];
+    packDGInOutDegreeMap(g, pairs, deg);
+    let start = -1;
+    for (const [node, ] of deg) { // looking for starting node
+        if (start == -1 || deg.get(node) == 1) start = node;
+    }
+    let path = eulerianPath(g, start);
+    path.reverse();
+    for (let i = 1; i < path.length; i++) {
+       res.push([path[i-1], path[i]]);
+    }
+    return res;
+};
+
+const eulerianPath = (g, start) => { // eulerian Path with Hierholzer’s Algorithm
+    let st = [start], path = [];
+    while (st.length) {
+        let u = st[st.length - 1], ua = g.get(u) || [];
+        if (ua.length) {
+            let v = ua.pop();
+            g.set(u, ua);
+            st.push(v);
+        } else {
+            path.push(u);
+            st.pop();
+        }
+    }
+    return path;
+};