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Commit 1a6b932

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--update : add A* algo
1 parent 6f31fb4 commit 1a6b932

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‎src/PathFinder/AStart/index.js‎

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/**
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* h is calculate by Euclidean Distance.
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* Complexity can be imporved by using Min-heap.
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* Worse case time complexity is O(E), where E is the number of edges in the graph.
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* Read more: [http://theory.stanford.edu/~amitp/GameProgramming/AStarComparison.html]
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*/
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function AStar(s, e, row, col, inputGrid) {
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const Row = row;
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const Col = col;
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const start = s;
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const end = e;
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function cell() {
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this.cellValue = null;
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this.parent_i = -1;
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this.parent_j = -1;
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this.h = Number.MAX_SAFE_INTEGER;
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this.g = Number.MAX_SAFE_INTEGER;
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this.f = Number.MAX_SAFE_INTEGER;
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}
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function pair(i, j, f) {
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this.i = i;
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this.j = j;
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this.f = f;
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}
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const grid = [];
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for (let i = 0; i < Row; i += 1) {
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grid[i] = [];
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for (let j = 0; j < Col; j += 1) {
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grid[i][j] = new cell();
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grid[i][j].cellValue = inputGrid[i][j];
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}
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}
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const isValid = (i, j) => i >= 0 && j >= 0 && i < Row && j < Col;
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const isDestination = (i, j) => end.i === i && end.j === j;
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const isBlocked = (i, j) => grid[i][j].cellValue === 0;
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const euclideanDistance = (i, j) => Math.abs(i - end.i) * Math.abs(i - end.i)
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+ Math.abs(j - end.j) * Math.abs(j - end.j);
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const trace = () => {
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const endRow = end.i;
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const endCol = end.j;
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const startRow = start.i;
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const startCol = start.j;
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let i = endRow;
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let j = endCol;
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const path = [];
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while (!(i === startRow && j === startCol)) {
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path.push([i, j]);
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const nextI = grid[i][j].parent_i;
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const nextJ = grid[i][j].parent_j;
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i = nextI;
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j = nextJ;
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}
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path.push([i, j]);
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for (let i = 0; i < path.length; i += 1) {
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console.log(path[i]);
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}
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};
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const neighbourExplorer = (i, j, parentI, parentJ, openList, openListMap,
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closedListMap, distanceFromParent) => {
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if (!isValid(i, j)) {
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return false;
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}
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if (isBlocked(i, j)) {
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return false;
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}
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if (isDestination(i, j)) {
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grid[i][j].parent_i = parentI;
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grid[i][j].parent_j = parentJ;
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trace();
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return true;
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}
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const g = grid[parentI][parentJ].g + distanceFromParent;
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const h = euclideanDistance(i, j);
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const f = g + h;
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if ((openListMap[[i, j]] && openListMap[[i, j]] > f)
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|| (closedListMap[[i, j]] && closedListMap[[i, j]] > f)
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|| (!closedListMap[[i, j]] && !openListMap[[i, j]])) {
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openListMap[[i, j]] = f;
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grid[i][j].parent_i = parentI;
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grid[i][j].parent_j = parentJ;
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grid[i][j].g = g;
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grid[i][j].h = h;
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grid[i][j].f = g + h;
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const item = new pair(i, j, f);
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// can be improved by using Min-Heap DataStructure
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if (!openList.length) {
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openList.push(item);
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}
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let k = 0;
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let temp = item;
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for (; k < openList.length; k += 1) {
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if (openList[k].f > item.f) {
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[temp, openList[k]] = [openList[k], temp];
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}
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}
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openList[k] = temp;
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}
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return false;
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};
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const search = () => {
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if (!isValid(start.i, start.j) || !isValid(end.i, end.j)) {
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return false;
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}
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let i = start.i;
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let j = start.j;
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const openList = [];
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const openListMap = new Map();
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const closedListMap = new Map();
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let foundDest = false;
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// Initialize start point
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grid[i][j].h = 0;
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grid[i][j].g = 0;
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grid[i][j].f = 0;
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openList.push(new pair(i, j, 0.0));
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openListMap[[i, j]] = 0;
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while (openList.length > 0) {
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const currentCell = openList.shift();
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i = currentCell.i;
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j = currentCell.j;
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const currentF = currentCell.f;
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closedListMap[[i, j]] = currentF;
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const parentI = i;
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const parentJ = j;
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foundDest = neighbourExplorer(i - 1, j, parentI, parentJ, openList, openListMap, closedListMap, 1); // for North
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if (foundDest) { break; }
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foundDest = neighbourExplorer(i, j - 1, parentI, parentJ, openList, openListMap, closedListMap, 1); // for West
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if (foundDest) { break; }
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foundDest = neighbourExplorer(i + 1, j, parentI, parentJ, openList, openListMap, closedListMap, 1); // for South
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if (foundDest) { break; }
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foundDest = neighbourExplorer(i, j + 1, parentI, parentJ, openList, openListMap, closedListMap, 1); // for East
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if (foundDest) { break; }
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foundDest = neighbourExplorer(i - 1, j - 1, parentI, parentJ, openList, openListMap, closedListMap, 1); // for N.W
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if (foundDest) { break; }
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foundDest = neighbourExplorer(i - 1, j + 1, parentI, parentJ, openList, openListMap, closedListMap, 1);// for S.W
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if (foundDest) { break; }
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foundDest = neighbourExplorer(i + 1, j + 1, parentI, parentJ, openList, openListMap, closedListMap, 1);// for S.E
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if (foundDest) { break; }
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foundDest = neighbourExplorer(i + 1, j - 1, parentI, parentJ, openList, openListMap, closedListMap, 1);// for N.E
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if (foundDest) { break; }
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}
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if (!foundDest) {
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return false;
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}
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return true;
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};
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search();
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}
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// const inputGrid = [
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// [1, 0, 1, 1, 1, 1, 0, 1, 1, 1],
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// [1, 1, 1, 0, 1, 1, 1, 0, 1, 1],
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// [1, 1, 1, 0, 1, 1, 0, 1, 0, 1],
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// [0, 0, 1, 0, 1, 0, 0, 0, 0, 1],
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// [1, 1, 1, 0, 1, 1, 1, 0, 1, 0],
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// [1, 0, 1, 1, 1, 1, 0, 1, 0, 0],
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// [1, 0, 0, 0, 0, 1, 0, 0, 0, 1],
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// [1, 0, 1, 1, 1, 1, 0, 1, 1, 1],
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// [1, 1, 1, 0, 0, 0, 1, 0, 0, 1],
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// ];
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const inputGrid = [
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[1, 0, 0, 0, 0, 0],
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[1, 1, 1, 1, 1, 1],
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[1, 0, 0, 0, 0, 0],
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[1, 1, 1, 1, 1, 1],
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];
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const ROW = inputGrid.length;
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const COL = inputGrid[0].length;
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const start = {
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i: 0,
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j: 0,
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};
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const end = {
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i: 3,
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j: 5,
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};
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AStar(start, end, ROW, COL, inputGrid);
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module.exports = {
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AStar,
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};

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