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leetcode_java/src/main/java/LeetCodeJava/Greedy/Candy.java
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| package LeetCodeJava.Greedy; | ||
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| // https://leetcode.com/problems/candy/ | ||
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| import java.util.Arrays; | ||
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| public class Candy { | ||
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| // V0 | ||
| // IDEA : GREEDY | ||
| // https://www.bilibili.com/video/BV1ev4y1r7wN/?share_source=copy_web&vd_source=49348a1975630e1327042905e52f488a | ||
| // TODO : fix it | ||
| // public int candy(int[] ratings) { | ||
| // | ||
| // if (ratings == null || ratings.length == 0){ | ||
| // return 0; | ||
| // } | ||
| // | ||
| // int ans = 0; | ||
| // int[] tmp = new int[]{}; | ||
| // for (int i = 0; i < ratings.length; i++){ | ||
| // tmp[i] = 1; | ||
| // } | ||
| // | ||
| // /** TIPS : DEAL WITH 1 DIRECTION AT ONCE */ | ||
| // | ||
| // // step 1) loop from left (compare element left) | ||
| // for (int j = 1; j < ratings.length-1; j++){ | ||
| // if (ratings[j] > ratings[j-1]){ | ||
| // tmp[j] += 1; | ||
| // } | ||
| // } | ||
| // | ||
| // // step 2) loop from right | ||
| // for (int k = ratings.length-2; k >= 0; k--){ | ||
| // if (ratings[k] > ratings[k+1]){ | ||
| // tmp[k] += 1; | ||
| // } | ||
| // } | ||
| // | ||
| // // step 3) get sum | ||
| // for (int z=0; z < tmp.length; z ++){ | ||
| // ans += tmp[z]; | ||
| // } | ||
| // | ||
| // return ans; | ||
| // } | ||
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| // V1 | ||
| // IDEA : BRUTE FORCE | ||
| // https://leetcode.com/problems/candy/editorial/ | ||
| public int candy_2(int[] ratings) { | ||
| int[] candies = new int[ratings.length]; | ||
| Arrays.fill(candies, 1); | ||
| boolean hasChanged = true; | ||
| while (hasChanged) { | ||
| hasChanged = false; | ||
| for (int i = 0; i < ratings.length; i++) { | ||
| if (i != ratings.length - 1 && ratings[i] > ratings[i + 1] && candies[i] <= candies[i + 1]) { | ||
| candies[i] = candies[i + 1] + 1; | ||
| hasChanged = true; | ||
| } | ||
| if (i > 0 && ratings[i] > ratings[i - 1] && candies[i] <= candies[i - 1]) { | ||
| candies[i] = candies[i - 1] + 1; | ||
| hasChanged = true; | ||
| } | ||
| } | ||
| } | ||
| int sum = 0; | ||
| for (int candy : candies) { | ||
| sum += candy; | ||
| } | ||
| return sum; | ||
| } | ||
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| // V2 | ||
| // IDEA : Using two arrays | ||
| // https://leetcode.com/problems/candy/editorial/ | ||
| public int candy_3(int[] ratings) { | ||
| int sum = 0; | ||
| int[] left2right = new int[ratings.length]; | ||
| int[] right2left = new int[ratings.length]; | ||
| Arrays.fill(left2right, 1); | ||
| Arrays.fill(right2left, 1); | ||
| for (int i = 1; i < ratings.length; i++) { | ||
| if (ratings[i] > ratings[i - 1]) { | ||
| left2right[i] = left2right[i - 1] + 1; | ||
| } | ||
| } | ||
| for (int i = ratings.length - 2; i >= 0; i--) { | ||
| if (ratings[i] > ratings[i + 1]) { | ||
| right2left[i] = right2left[i + 1] + 1; | ||
| } | ||
| } | ||
| for (int i = 0; i < ratings.length; i++) { | ||
| sum += Math.max(left2right[i], right2left[i]); | ||
| } | ||
| return sum; | ||
| } | ||
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| // V3 | ||
| // IDEA : Using one array | ||
| // https://leetcode.com/problems/candy/editorial/ | ||
| public int candy_4(int[] ratings) { | ||
| int[] candies = new int[ratings.length]; | ||
| Arrays.fill(candies, 1); | ||
| for (int i = 1; i < ratings.length; i++) { | ||
| if (ratings[i] > ratings[i - 1]) { | ||
| candies[i] = candies[i - 1] + 1; | ||
| } | ||
| } | ||
| int sum = candies[ratings.length - 1]; | ||
| for (int i = ratings.length - 2; i >= 0; i--) { | ||
| if (ratings[i] > ratings[i + 1]) { | ||
| candies[i] = Math.max(candies[i], candies[i + 1] + 1); | ||
| } | ||
| sum += candies[i]; | ||
| } | ||
| return sum; | ||
| } | ||
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| // V4 | ||
| // IDEA : Single Pass Approach with Constant Space | ||
| // https://leetcode.com/problems/candy/editorial/ | ||
| public int count(int n) { | ||
| return (n * (n + 1)) / 2; | ||
| } | ||
| public int candy_5(int[] ratings) { | ||
| if (ratings.length <= 1) { | ||
| return ratings.length; | ||
| } | ||
| int candies = 0; | ||
| int up = 0; | ||
| int down = 0; | ||
| int oldSlope = 0; | ||
| for (int i = 1; i < ratings.length; i++) { | ||
| int newSlope = (ratings[i] > ratings[i - 1]) ? 1 | ||
| : (ratings[i] < ratings[i - 1] ? -1 | ||
| : 0); | ||
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| if ((oldSlope > 0 && newSlope == 0) || (oldSlope < 0 && newSlope >= 0)) { | ||
| candies += count(up) + count(down) + Math.max(up, down); | ||
| up = 0; | ||
| down = 0; | ||
| } | ||
| if (newSlope > 0) { | ||
| up++; | ||
| } else if (newSlope < 0) { | ||
| down++; | ||
| } else { | ||
| candies++; | ||
| } | ||
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| oldSlope = newSlope; | ||
| } | ||
| candies += count(up) + count(down) + Math.max(up, down) + 1; | ||
| return candies; | ||
| } | ||
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| } |