08.27: tree, divide-conquer, recursion(트리)

baekjoon/4256.js

@@ -0,0 +1,52 @@
+// 트리 : 트리, 분할 정복, 재귀
+const input = require("fs")
+  .readFileSync(0, "utf-8")
+  .toString()
+  .trim()
+  .split("\n")
+  .map((v) => v.split(" ").map((v) => Number(v)));
+const [t] = input[0];
+const answer = [];
+let i = 0;
+
+function recur(preOrder, inOrder, n, result) {
+  let [preRoot, preLeft, preRight] = [preOrder[0], [], []];
+  let [inRoot, inLeft, inRight] = [0, [], []];
+
+  if (preOrder.length === 1) {
+    result.push(preOrder[0]);
+    return;
+  } else if (preOrder.length === 0) {
+    return;
+  }
+
+  // slice에서 마지막에 n을 넣지 않았더니 틀렸다고 나옴
+  // why?
+  // n개 보다 더 많은 경우가 있는가?
+  for (let a = 0; a < inOrder.length; a++) {
+    if (inOrder[a] === preRoot) {
+      inRoot = preRoot;
+      inLeft = inOrder.slice(0, a);
+      inRight = inOrder.slice(a + 1, n);
+      preLeft = preOrder.slice(1, a + 1);
+      preRight = preOrder.slice(a + 1, n);
+      break;
+    }
+  }
+  recur(preLeft, inLeft, preLeft.length, result); // left
+  recur(preRight, inRight, preRight.length, result); // right
+  result.push(preRoot); // root
+}
+
+while (i < t) {
+  const offset = 3 * i;
+  const [n] = input[1 + offset];
+  const preOrder = input[2 + offset];
+  const inOrder = input[3 + offset];
+  const result = [];
+  recur(preOrder, inOrder, n, result);
+  answer.push(result.join(" "));
+  i++;
+}
+
+console.log(answer.join("\n"));