Day 11 - optimise partial sum

Author: stevenhorsman

day-11-chronal-change/fuelcells.js

@@ -1,19 +1,16 @@
-class FuelCellGrid {
+class SummedAreaTable {
   constructor(serialNo, length = 300, subsectionSize = 3) {
     this.serial = serialNo;
     this.length = length;
     this.subsectionSize = subsectionSize;
-    this.grid = Array
+    this.sum = Array
       .from({ length })
       .map(() => Array
         .from({ length }));
-    for(let x = 0; x < 300; x++) {
-      for(let y = 0; y < 300; y++) {
-        this.grid[x][y] = calculateFuelCellValue(this.serial, x+1, y+1);
-        if(x >=32 && x<=34 && y>=44 && y <= 46) {
-          // console.log(calculateFuelCellValue(this.serial, x+1, y+1),'=',this.getValue(x,y));
-        }
-      //getGridValue(grid,32,44);
+    for(let y = 0; y < length; y++) {
+      for(let x = 0; x < length; x++) {
+        this.sum[y][x] = calculateFuelCellValue(this.serial, x+1, y+1) + this.getSumValue(y - 1,x) + this.getSumValue(y,x - 1) - this.getSumValue(y - 1,x - 1);
+        //console.log(x,y,':',calculateFuelCellValue(this.serial, x+1, y+1), '+', this.getSumValue(y - 1,x), '+', this.getSumValue(y,x - 1) ,'-', this.getSumValue(y - 1,x - 1),'=',this.sum[y][x]);
       }
     }
   }
@@ -23,32 +20,30 @@ class FuelCellGrid {
     let coord;
     for(let x = 0; x < this.length-size; x++) {
       for(let y = 0; y < this.length-size; y++) {
-        let curr = this.sumSubSection(x, y,size);
+        let curr = this.sumSubSection(y, x,size);
         if (curr > currMax) {
           currMax = curr;
-          coord = `${x+1},${y+1}`;
+          coord = `${x+2},${y+2}`;//no idea why this is +2 rather than +1!
         }
       }
     }
     return {coord:coord, power:currMax};
   }
 
-  sumSubSection(xStart, yStart,size=this.subsectionSize) {
-    let sum = 0;
-    for(let x = 0; x < size; x++) {
-      for(let y = 0; y < size; y++) {
-        sum += this.grid[x+xStart][y+yStart];
-      }
+  sumSubSection(y, x,size=this.subsectionSize) {
+    return this.sum[y][x] + this.sum[y + size][x + size] - this.sum[y + size][x] - this.sum[y][x + size];
+  }
+
+  getSumValue(y,x) {
+    if (x < 0 || y < 0) {
+      return 0;
     }
-    return sum;
+    return this.sum[y][x];
   }
 
   getValue(x,y) {
-    let value = this.grid[x][y];
-    console.log(`${x+1},${y+1}=${value}`);
-    return value;
+    return this.sumSubSection(y-1,x-1,1);
   }
-
 }
 
 function calculateFuelCellValue(serial, x, y) {
@@ -63,23 +58,38 @@ function getHundredsValue(input) {
 }
 
 function calculateMaxFuelGrid3(serial) {
-  const grid = new FuelCellGrid(serial);
+  const grid = new SummedAreaTable(serial);
   return grid.getMaxSubSectionCoordinate().coord;
 }
 
 function calculateMaxFuelGrid(serial) {
-  const grid = new FuelCellGrid(serial);
+  const grid = new SummedAreaTable(serial);
 
   const maxPowers = [];
   for(let i = 1; i <= 300; i++) {
+    //console.log(i);
     let max_i = grid.getMaxSubSectionCoordinate(i);
     maxPowers.push({size:i,coord:max_i.coord, power:max_i.power});
   }
   let max = maxPowers.sort((a, b) => b.power - a.power)[0];
+  //console.log(maxPowers);
+  return max.coord + ',' + max.size;
+}
 
+function calculateMaxFuelSum(serial) {
+  const sum = new SummedAreaTable(serial);
+  const maxPowers = [];
+  for(let i = 1; i <= 300; i++) {
+    //console.log(i);
+    let max_i = sum.getMaxSubSectionCoordinate(i);
+    maxPowers.push({size:i,coord:max_i.coord, power:max_i.power});
+  }
+  let max = maxPowers.sort((a, b) => b.power - a.power)[0];
+  //console.log(maxPowers);
   return max.coord + ',' + max.size;
 }
 
 module.exports.calculateFuelCellValue = calculateFuelCellValue;
 module.exports.calculateMaxFuelGrid3 = calculateMaxFuelGrid3;
-module.exports.calculateMaxFuelGrid = calculateMaxFuelGrid;
+module.exports.calculateMaxFuelGrid = calculateMaxFuelGrid;
+module.exports.calculateMaxFuelSum = calculateMaxFuelSum;

day-11-chronal-change/test.js

@@ -2,7 +2,7 @@ const expect = require('chai').expect;
 
 const fuelcells = require('./fuelcells');
 
-describe('Day 11: Chronal Charge', () => {
+describe.only('Day 11: Chronal Charge', () => {
 
   describe('Calculate fuel cell value', () => {
     it('fuel cell at 3,5 in a grid with serial number 8', () => {
@@ -30,9 +30,11 @@ describe('Day 11: Chronal Charge', () => {
   describe('Part One', () => {
     // it('print grid 33,45, serial 18', () => {
     //   let serial = 18;
-    //   for(let y = 45;y<45+3;y++) {
+    //   let xStart = 1;
+    //   let yStart = 1;
+    //   for(let y = yStart;y<yStart+3;y++) {
     //     let row = [];
-    //     for(let x = 33;x<33+3;x++) {
+    //     for(let x = xStart;x<xStart+3;x++) {
     //       row.push(fuelcells.calculateFuelCellValue(serial, x, y));
     //     }
     //     console.log(row.join(' '));
@@ -52,17 +54,17 @@ describe('Day 11: Chronal Charge', () => {
     });
   });
 
-  describe.only('Part Two', () => {
+  describe('Part Two', () => {    
     it('should get x,y of largest total power for serial number 18', () => {
-      expect(fuelcells.calculateMaxFuelGrid(18)).to.equal('90,269,16');
+      expect(fuelcells.calculateMaxFuelSum(18)).to.equal('90,269,16');
     }).timeout(500000);
 
     it('should get x,y of largest total power for serial number 42', () => {
-      expect(fuelcells.calculateMaxFuelGrid(42)).to.equal('232,251,12');
+      expect(fuelcells.calculateMaxFuelSum(42)).to.equal('232,251,12');
     }).timeout(500000);
 
     it('should get x,y of largest total power for serial number 2187', () => {
-      expect(fuelcells.calculateMaxFuelGrid(2187)).to.equal('233,40,13');
+      expect(fuelcells.calculateMaxFuelSum(2187)).to.equal('233,40,13');
     }).timeout(500000);
   });
 });