-
Notifications
You must be signed in to change notification settings - Fork 0
Commit
This commit does not belong to any branch on this repository, and may belong to a fork outside of the repository.
- Loading branch information
1 parent
cfe9851
commit b5c115f
Showing
1 changed file
with
83 additions
and
0 deletions.
There are no files selected for viewing
This file contains bidirectional Unicode text that may be interpreted or compiled differently than what appears below. To review, open the file in an editor that reveals hidden Unicode characters.
Learn more about bidirectional Unicode characters
Original file line number | Diff line number | Diff line change |
---|---|---|
@@ -0,0 +1,83 @@ | ||
// 행렬 곱셈 순서 : 동적 계획법 | ||
const input = require("fs") | ||
.readFileSync("/dev/stdin") | ||
.toString() | ||
.trim() | ||
.split("\n"); | ||
const n = Number(input.shift()); | ||
const matrix = input.map((v) => v.split(" ").map((v) => Number(v))); | ||
const dp = new Array(n + 1).fill(null).map(() => new Array(n + 1).fill(0)); | ||
const result = new Array(n + 1).fill(null).map(() => new Array(n + 1).fill(0)); | ||
|
||
for (let i = 1; i <= n; i++) { | ||
result[i][i] = matrix[i - 1]; | ||
} | ||
|
||
// 대각선 방향 init | ||
for (let i = 1; i < n; i++) { | ||
dp[i][i + 1] = | ||
result[i][i][0] * result[i + 1][i + 1].reduce((acc, curr) => acc * curr, 1); | ||
result[i][i + 1] = [result[i][i][0], result[i + 1][i + 1][1]]; | ||
} | ||
|
||
// 대각선 방향 채우기 | ||
// - e.g. [1, 3], [2, 4] ... [1, 4] | ||
for (let i = 2; i < n; i++) { | ||
for (let j = 1; j + i <= n; j++) { | ||
let min = Infinity; | ||
let range = []; | ||
let count = end - start + 1; | ||
let [start, end] = [j, j + i]; | ||
// n개와 1개를 합치는 경우 | ||
const candidates = [ | ||
[start, end - 1], | ||
[start + 1, end], | ||
]; | ||
for (let k = 0; k < 2; k++) { | ||
const [s, e] = candidates[k]; | ||
let prev, curr; | ||
if (k === 0) { | ||
prev = result[s][e]; | ||
curr = matrix[e]; | ||
} else { | ||
prev = matrix[s - 2]; | ||
curr = result[s][e]; | ||
} | ||
const res = | ||
dp[s][e] + prev[0] * curr.reduce((acc, curr) => acc * curr, 1); | ||
if (min > res) { | ||
min = res; | ||
range = [prev[0], curr[1]]; | ||
} | ||
} | ||
// n개와 m개를 합치는 경우 | ||
const candidates2 = []; | ||
for (let k = 2; k <= count - 2; k++) { | ||
candidates2.push([k, count - k]); | ||
} | ||
for (const [s, e] of candidates2) { | ||
const prev = result[start][end - s]; | ||
const curr = result[start + e][end]; | ||
const res = | ||
dp[start][end - s] + | ||
dp[start + e][end] + | ||
prev[0] * curr.reduce((acc, curr) => acc * curr, 1); | ||
if (min > res) { | ||
min = res; | ||
range = [prev[0], curr[1]]; | ||
} | ||
} | ||
dp[start][end] = min; | ||
result[start][end] = range; | ||
} | ||
} | ||
|
||
console.log(dp[1][n]); | ||
|
||
// 114'13" | ||
|
||
// dp 테이블 : row 부터 column 까지 최소 곱셈 횟수 | ||
// [1, 5]의 최소 곱셈 횟수를 구하는 방법은 | ||
// - [1, 4], [5] / [1, 3], [4, 5] / [1, 2], [3, 5] / [1], [2, 5] | ||
// - 각각의 범위는 미리 구해놓아야 함 | ||
// - 대각선 방향으로 초기화하면 됨 |