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| 20231106: 134 | ||
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| 20231006: quick_sort,286 | ||
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94 changes: 94 additions & 0 deletions
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leetcode_java/src/main/java/LeetCodeJava/Greedy/GasStation.java
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| @@ -0,0 +1,94 @@ | ||
| package LeetCodeJava.Greedy; | ||
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| // https://leetcode.com/problems/gas-station/ | ||
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| import java.util.ArrayList; | ||
| import java.util.List; | ||
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| public class GasStation { | ||
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| // VO | ||
| // IDEA: GREEDY | ||
| // https://www.bilibili.com/video/BV1jA411r7WX/?share_source=copy_web&vd_source=49348a1975630e1327042905e52f488a | ||
| /** | ||
| * total_gain = gain1 + gain2 + .... | ||
| * | ||
| * if total_gain > 0, then gain1 + gain2 + ... >= 0 | ||
| * | ||
| * then gain1 >= - (gain2 + gain3 + ...) | ||
| * | ||
| * -> means car start from such idx (gain1) is ENOUGH to visit all stops | ||
| * | ||
| */ | ||
| public int canCompleteCircuit(int[] gas, int[] cost) { | ||
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| if (gas == null || cost == null || gas.length == 0 || cost.length == 0){ | ||
| return 0; | ||
| } | ||
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| int remain = 0; | ||
| int total = 0; | ||
| int start = 0; | ||
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| for (int i = 0; i < gas.length; i++){ | ||
| remain += (gas[i] - cost[i]); | ||
| // keep maintaining total, since NEED to know whether this start point can finish visit all stops | ||
| // example : we start again on idx = 3, still need to know if car can go idx = 3, 4 ... N .. 0 and back to 3 | ||
| total += (gas[i] - cost[i]); | ||
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| if (remain < 0){ | ||
| remain = 0; | ||
| start = i+1; | ||
| } | ||
| } | ||
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| return total < 0 ? -1 : start; | ||
| } | ||
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| // public int canCompleteCircuit(int[] gas, int[] cost) { | ||
| // | ||
| // if (gas == null || cost == null || gas.length == 0 || cost.length == 0){ | ||
| // return 0; | ||
| // } | ||
| // | ||
| // List<Integer> diffList = new ArrayList(); | ||
| // | ||
| // diffList.add(gas[1] - cost[cost.length-1]); | ||
| // | ||
| // for (int i = 1; i < gas.length; i++){ | ||
| // int diff = gas[i] - cost[i-1]; | ||
| // diffList.add(diff); | ||
| // } | ||
| // | ||
| // // reset start point if current sum < diff | ||
| // for (int i = 0; i < diffList.size(); i++){ | ||
| // if (diffList.get(i) > 0){ | ||
| // return i; | ||
| // } | ||
| // } | ||
| // return -1; | ||
| // } | ||
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| // V1 | ||
| // IDEA : ONE PASS | ||
| // https://leetcode.com/problems/gas-station/editorial/ | ||
| public int canCompleteCircuit_2(int[] gas, int[] cost) { | ||
| int currGain = 0, totalGain = 0, answer = 0; | ||
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| for (int i = 0; i < gas.length; ++i) { | ||
| // gain[i] = gas[i] - cost[i] | ||
| totalGain += gas[i] - cost[i]; | ||
| currGain += gas[i] - cost[i]; | ||
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| // If we meet a "valley", start over from the next station | ||
| // with 0 initial gas. | ||
| if (currGain < 0) { | ||
| answer = i + 1; | ||
| currGain = 0; | ||
| } | ||
| } | ||
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| return totalGain >= 0 ? answer : -1; | ||
| } | ||
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| } |
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| package dev; | ||
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| public class workSpace2 { | ||
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| public static void main(String[] args) { | ||
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| // Integer[] my_list = new Integer[0]; | ||
| // for (int i = 0; i < my_list.length; i++){ | ||
| // System.out.println(my_list[i]); | ||
| // | ||
| // Integer.parseInt("1"); | ||
| // | ||
| // } | ||
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| String x = "abcd"; | ||
| System.out.println(x.substring(1,3)); | ||
| StringBuilder sb = new StringBuilder(x.substring(1,3)); | ||
| System.out.println(sb.reverse()); | ||
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| System.out.println(x.substring(x.length()-1, x.length())); | ||
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| } | ||
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| } |