|531|[Lonely Pixel I](https://leetcode.com/problems/lonely-pixel-i/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_531.java)||Medium|

|530|[Minimum Absolute Difference in BST](https://leetcode.com/problems/minimum-absolute-difference-in-bst/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_530.java) | |Easy| DFS

|529|[Minesweeper](https://leetcode.com/problems/minesweeper/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_529.java) | |Medium | BFS

|528|[Random Pick with Weight](https://leetcode.com/problems/random-pick-with-weight/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_528.java) | |Medium | Math, Binary Search, Prefix Sum, Randomized

|527|[Word Abbreviation](https://leetcode.com/problems/word-abbreviation/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_527.java)||Hard|

|526|[Beautiful Arrangement](https://leetcode.com/problems/beautiful-arrangement/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_526.java) | |Medium | Backtracking

|525|[Contiguous Array](https://leetcode.com/problems/contiguous-array/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_525.java) | |Medium | HashMap

packagecom.fishercoder.solutions;

importjava.util.Random;

publicclass_528 {

publicstaticclassSolution1 {

Randomrandom;

int[]preSums;

publicSolution1(int[]w) {

this.random =newRandom();

for (inti =1;i <w.length; ++i) {

w[i] +=w[i -1];

}

this.preSums =w;

}

publicintpickIndex() {

intlen =preSums.length;

intidx =random.nextInt(preSums[len -1]) +1;

intleft =0,right =len -1;

while (left <right) {

intmid =left + (right -left) /2;

if (preSums[mid] ==idx)

returnmid;

elseif (preSums[mid] <idx)

left =mid +1;

right =mid;

}

returnleft;

}

}

}

packagecom.fishercoder;

importcom.fishercoder.solutions._528;

importorg.junit.Test;

importstaticorg.junit.Assert.assertEquals;

publicclass_528Test {

privatestatic_528.Solution1solution1;

privatestaticintexpected;

publicvoidtest1() {

solution1 =new_528.Solution1(newint[]{1});

expected =0;

assertEquals(expected,solution1.pickIndex());

}

publicvoidtest2() {

solution1 =new_528.Solution1(newint[]{1,3});

System.out.println(solution1.pickIndex());

System.out.println(solution1.pickIndex());

System.out.println(solution1.pickIndex());

System.out.println(solution1.pickIndex());

System.out.println(solution1.pickIndex());

}

}