docs: 세그먼트 트리 예시 추가

Author: HyunJinNo

_posts/2024-05-21-segment-tree.md

@@ -286,7 +286,84 @@ console.log(query(3, 5, 1, 0, arr.length - 1)); // 8 + 9 + 11 = 28
 
 ## Example
 
-- <a href="" target="_blank">TODO</a>
+- <a href="https://www.acmicpc.net/problem/11505" target="_blank">11505번: 구간 곱 구하기</a>
+
+  ```javascript
+  const path = process.platform === "linux" ? "/dev/stdin" : "input.txt";
+  const input = require("fs").readFileSync(path).toString().split("\n");
+
+  // N: 수의 개수, 1 <= N <= 1_000_000
+  // M: 수의 변경이 일어나는 횟수, 1 <= M <= 10_000
+  // K: 구간 곱을 구하는 횟수, 1 <= K <= 10_000
+  const [N, M, K] = input[0].split(" ").map(Number);
+  const MOD = 1_000_000_007n;
+  const arr = [];
+
+  for (let i = 1; i <= N; i++) {
+    arr.push(Number(input[i]));
+  }
+
+  const tree = Array(arr.length * 4);
+
+  const init = (left, right, node) => {
+    if (left === right) {
+      tree[node] = BigInt(arr[left]);
+      return;
+    }
+
+    const mid = Math.floor((left + right) / 2);
+    init(left, mid, node * 2);
+    init(mid + 1, right, node * 2 + 1);
+    tree[node] = (tree[node * 2] * tree[node * 2 + 1]) % MOD;
+  };
+
+  const query = (left, right, node, nodeLeft, nodeRight) => {
+    if (right < nodeLeft || nodeRight < left) {
+      return 1n;
+    }
+
+    if (left <= nodeLeft && nodeRight <= right) {
+      return tree[node];
+    }
+
+    const mid = Math.floor((nodeLeft + nodeRight) / 2);
+    const leftResult = query(left, right, node * 2, nodeLeft, mid);
+    const rightResult = query(left, right, node * 2 + 1, mid + 1, nodeRight);
+    return (leftResult * rightResult) % MOD;
+  };
+
+  const update = (index, newValue, node, nodeLeft, nodeRight) => {
+    if (index < nodeLeft || nodeRight < index) {
+      return;
+    }
+
+    if (nodeLeft === nodeRight) {
+      tree[node] = BigInt(newValue);
+      return;
+    }
+
+    const mid = Math.floor((nodeLeft + nodeRight) / 2);
+    update(index, newValue, node * 2, nodeLeft, mid);
+    update(index, newValue, node * 2 + 1, mid + 1, nodeRight);
+    tree[node] = (tree[node * 2] * tree[node * 2 + 1]) % MOD;
+  };
+
+  init(0, arr.length - 1, 1);
+
+  let answer = "";
+
+  for (let i = N + 1; i < N + M + K + 1; i++) {
+    const [a, b, c] = input[i].split(" ").map(Number);
+
+    if (a === 1) {
+      update(b - 1, c, 1, 0, arr.length - 1);
+    } else {
+      answer += `${query(b - 1, c - 1, 1, 0, arr.length - 1)}\n`;
+    }
+  }
+
+  console.log(answer.trim());
+  ```
 
 ## 참고 자료