|
2 | 2 | * @param {number[]} terraces |
3 | 3 | * @return {number} |
4 | 4 | */ |
5 | | - |
6 | | -/* |
7 | | - * STEPS |
8 | | - * 1. Find the highest terraces on the left and right side of the elevation map: |
9 | | - * e.g. [0, 2, 4, 3, 1, 2, 4, 0, 8, 7, 0] => (leftMax = 4, rightMax = 8) |
10 | | - * This is because water will "trail off" the sides of the terraces. |
11 | | - * |
12 | | - * 2. At this point, we are essentially dealing with a new map: [4, 3, 4, 2, 4, 0, 8]. |
13 | | - * From here, we loop through the map from the left to the right (if leftMax > rightMax, |
14 | | - * otherwise we move from right to left), adding water as we go unless we reach a value |
15 | | - * that is greater than or equal to leftMax || rightMax. |
16 | | - * e.g. [4, 3, 4, 2, 4, 0, 8] |
17 | | - * ^ |
18 | | - * water += leftMax - 3 => water = 1 |
19 | | - * or if the terrace array was reversed: |
20 | | - * e.g. [8, 0, 4, 2, 4, 3, 4] |
21 | | - * ^ |
22 | | - * water += rightMax - 3 => water = 1 |
23 | | - * |
24 | | - * 3. Again, we've essentially shortened the map: [4, 2, 4, 0, 8]. |
25 | | - * Now we repeat the above steps on the new array. |
26 | | - * e.g. |
27 | | - * Next Iteration: |
28 | | - * [4, 2, 4, 0, 8] |
29 | | - * ^ |
30 | | - * water += leftMax - 2 => water = 3 |
31 | | - * |
32 | | - * Next Iteration: |
33 | | - * [4, 0, 8] |
34 | | - * ^ |
35 | | - * water += leftMax - 0 => water = 7 |
36 | | - * |
37 | | - * return water(7) |
38 | | - */ |
39 | 5 | export default function rainTerraces(terraces) { |
40 | | - let start = 0; |
41 | | - let end = terraces.length - 1; |
42 | | - let water = 0; |
43 | | - let leftMax = 0; |
44 | | - let rightMax = 0; |
| 6 | + /* |
| 7 | + * STEPS |
| 8 | + * |
| 9 | + * 1. Find the highest terraces on the left and right side of the elevation map: |
| 10 | + * e.g. for [0, 2, 4, 3, 4, 2, 4, 0, 8, 7, 0] we would have leftMax = 4 and rightMax = 8. |
| 11 | + * This is because water will "trail off" the sides of the terraces. |
| 12 | + * |
| 13 | + * 2. At this point, we are essentially dealing with a new map: [4, 3, 4, 2, 4, 0, 8]. |
| 14 | + * From here, we loop through the map from the left to the right if leftMax < rightMax |
| 15 | + * (otherwise we move from right to left), adding water as we go unless we reach a value |
| 16 | + * that is greater than or equal to leftMax or rightMax. |
| 17 | + * e.g. [4, 3, 4, 2, 4, 0, 8] |
| 18 | + * ^ |
| 19 | + * water = water + (leftMax - 3) = 1 |
| 20 | + * |
| 21 | + * or if the terrace array was reversed: |
| 22 | + * e.g. [8, 0, 4, 2, 4, 3, 4] |
| 23 | + * ^ |
| 24 | + * water = water + (rightMax - 3) = 1 |
| 25 | + * |
| 26 | + * 3. Again, we've essentially shortened the map: [4, 2, 4, 0, 8]. |
| 27 | + * Now we repeat the above steps on the new array. |
| 28 | + * |
| 29 | + * Next Iteration: |
| 30 | + * [4, 2, 4, 0, 8] |
| 31 | + * ^ |
| 32 | + * water = water + (leftMax - 2) = 3 |
| 33 | + * |
| 34 | + * Next Iteration: |
| 35 | + * [4, 0, 8] |
| 36 | + * ^ |
| 37 | + * water = water + (leftMax - 0) = 7 |
| 38 | + * |
| 39 | + * 4. Return result: 7 |
| 40 | + */ |
| 41 | + let leftIndex = 0; |
| 42 | + let rightIndex = terraces.length - 1; |
| 43 | + |
| 44 | + let leftMaxLevel = 0; |
| 45 | + let rightMaxLevel = 0; |
45 | 46 |
|
46 | | - while (start < end) { |
47 | | - // Loop to find left max |
48 | | - while (start < end && terraces[start] <= terraces[start + 1]) { |
49 | | - start += 1; |
| 47 | + let waterAmount = 0; |
| 48 | + |
| 49 | + while (leftIndex < rightIndex) { |
| 50 | + // Loop to find the highest terrace from the left side. |
| 51 | + while (leftIndex < rightIndex && terraces[leftIndex] <= terraces[leftIndex + 1]) { |
| 52 | + leftIndex += 1; |
50 | 53 | } |
51 | | - leftMax = terraces[start]; |
52 | 54 |
|
53 | | - // Loop to find right max |
54 | | - while (end > start && terraces[end] <= terraces[end - 1]) { |
55 | | - end -= 1; |
| 55 | + leftMaxLevel = terraces[leftIndex]; |
| 56 | + |
| 57 | + // Loop to find the highest terrace from the right side. |
| 58 | + while (rightIndex > leftIndex && terraces[rightIndex] <= terraces[rightIndex - 1]) { |
| 59 | + rightIndex -= 1; |
56 | 60 | } |
57 | | - rightMax = terraces[end]; |
58 | 61 |
|
59 | | - // Determine which direction we need to move in |
60 | | - if (leftMax < rightMax) { |
61 | | - // Move from left to right and collect water |
62 | | - start += 1; |
63 | | - while (start < end && terraces[start] <= leftMax) { |
64 | | - water += leftMax - terraces[start]; |
65 | | - start += 1; |
| 62 | + rightMaxLevel = terraces[rightIndex]; |
| 63 | + |
| 64 | + // Determine which direction we need to go. |
| 65 | + if (leftMaxLevel < rightMaxLevel) { |
| 66 | + // Move from left to right and collect water. |
| 67 | + leftIndex += 1; |
| 68 | + |
| 69 | + while (leftIndex < rightIndex && terraces[leftIndex] <= leftMaxLevel) { |
| 70 | + waterAmount += leftMaxLevel - terraces[leftIndex]; |
| 71 | + leftIndex += 1; |
66 | 72 | } |
67 | 73 | } else { |
68 | | - // Move from left to right and collect water |
69 | | - end -= 1; |
70 | | - while (end > start && terraces[end] <= rightMax) { |
71 | | - water += rightMax - terraces[end]; |
72 | | - end -= 1; |
| 74 | + // Move from right to left and collect water. |
| 75 | + rightIndex -= 1; |
| 76 | + |
| 77 | + while (leftIndex < rightIndex && terraces[rightIndex] <= rightMaxLevel) { |
| 78 | + waterAmount += rightMaxLevel - terraces[rightIndex]; |
| 79 | + rightIndex -= 1; |
73 | 80 | } |
74 | 81 | } |
75 | 82 | } |
76 | | - return water; |
| 83 | + |
| 84 | + return waterAmount; |
77 | 85 | } |
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