A typescript implementation of the **ISAP (Improved SAP)** algorithm.
The **ISAP** algorithm is an algorithm for solving network flow problems.
## Install
- npm
```bash
npm install --save @algorithm.ts/isap
```
- yarn
```bash
yarn add @algorithm.ts/isap
```
## Usage
- Simple
```typescript
import { Isap } from '@algorithm.ts/isap'
const isap = createIsap()
isap.init(0, 1, 4)
isap.addEdge(0, 2, 1)
isap.addEdge(0, 3, 2)
isap.addEdge(3, 1, 1)
isap.maxFlow() // => 1
// Access current residual network.
class CustomIsap extends Isap {
public getSnapshot() {
return {
N: this._N,
source: this._source,
sink: this._sink,
G: this.G,
edges: this._edges,
edgesTot: this._edgesTot,
dist: this._dist
}
}
}
```
### Example
- A solution for Codeforces contest 1082 Problem G (https://codeforces.com/contest/1082/problem/G):
```typescript
import { Isap } from '@algorithm.ts/isap'
const isap = new Isap()
export function solveCodeforces1082G(
nodes: number[],
edges: Array<[u: number, v: number, weight: number]>,
): number {
const n: number = nodes.length
const m: number = edges.length
const source = 0
const target: number = n + m + 1
isap.init(source, target, n + m + 2)
for (let i = 0; i < n; ++i) {
const weight: number = nodes[i]
isap.addEdge(i + 1, target, weight)
}
let answer = 0
for (let i = 0; i < m; ++i) {
const [u, v, weight] = edges[i]
const x = n + i
answer += weight
isap.addEdge(source, x, weight)
isap.addEdge(x, u, Number.MAX_SAFE_INTEGER)
isap.addEdge(x, v, Number.MAX_SAFE_INTEGER)
}
answer -= isap.maxflow()
return answer
}
```
- A solution for leetcode "Maximum Students Taking Exam"
(https://leetcode.com/problems/maximum-students-taking-exam/):
```typescript
import { Isap } from '@algorithm.ts/isap'
export function maxStudents(seats: string[][]): number {
const R: number = seats.length
if (R <= 0) return 0
const C: number = seats[0].length
if (C <= 0) return 0
let total = 0
const seatCodes: number[][] = new Array(R)
for (let r = 0; r < R; ++r) seatCodes[r] = new Array(C).fill(-1)
for (let r = 0; r < R; ++r) {
for (let c = 0; c < C; ++c) {
if (seats[r][c] === '.') seatCodes[r][c] = total++
}
}
if (total <= 0) return 0
if (total === 1) return 1
const source: number = total * 2
const target: number = source + 1
isap.init(source, target, target + 1)
for (let r = 0; r < R; ++r) {
for (let c = 0; c < C; ++c) {
const u: number = seatCodes[r][c]
if (u > -1) {
isap.addEdge(source, u, 1)
isap.addEdge(u + total, target, 1)
if (r > 0) {
// Check upper left
if (c > 0 && seatCodes[r - 1][c - 1] > -1) {
const v: number = seatCodes[r - 1][c - 1]
isap.addEdge(u, v + total, 1)
isap.addEdge(v, u + total, 1)
}
// Check upper right
if (c + 1 < C && seatCodes[r - 1][c + 1] > -1) {
const v: number = seatCodes[r - 1][c + 1]
isap.addEdge(u, v + total, 1)
isap.addEdge(v, u + total, 1)
}
}
// Check left
if (c > 0 && seatCodes[r][c - 1] > -1) {
const v: number = seatCodes[r][c - 1]
isap.addEdge(u, v + total, 1)
isap.addEdge(v, u + total, 1)
}
}
}
}
const totalPaired: number = isap.maxflow() / 2
return total - totalPaired
}
```
## Related
- [@algorithm.ts/isap](https://github.com/guanghechen/algorithm.ts/tree/@algorithm.ts/isap@4.0.4/packages/isap)
- [@algorithm.ts/mcmf](https://github.com/guanghechen/algorithm.ts/tree/@algorithm.ts/mcmf@4.0.4/packages/mcmf)
- [网络流 24 题](https://me.guanghechen.com/post/algorithm/graph/network-flow/24-problems/)
- [网络流基础之最大权闭合图](https://me.guanghechen.com/post/algorithm/graph/network-flow/%E6%9C%80%E5%A4%A7%E6%9D%83%E9%97%AD%E5%90%88%E5%9B%BE/)
[homepage]:
https://github.com/guanghechen/algorithm.ts/tree/@algorithm.ts/isap@4.0.4/packages/isap#readme
