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BinarySearch.java
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126 lines (115 loc) · 3.54 KB
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package problems;
/**
* 二分查找
*/
public class BinarySearch {
public static int search(int[] arr, int val) {
int low = 0, high = arr.length - 1, mid;
while (low <= high) {
// 如果数组很大，low + high可能会发生溢出
mid = low + (high - low)/2;
if (arr[mid] == val) return mid;
if (arr[mid] < val) {
low = mid + 1;
} else {
high = mid - 1;
}
}
return -1;
}
/**
* 查找第一个值等于给定值的索引
*/
public static int searchFirst(int[] arr, int val) {
int low = 0, high = arr.length - 1, mid;
while (low <= high) {
// 如果数组很大，low + high可能会发生溢出
mid = low + (high - low)/2;
if (arr[mid] < val) {
low = mid + 1;
} else if (arr[mid] > val) {
high = mid - 1;
} else {
// 判断是否第一个位置
if (mid == 0 || (arr[mid - 1] != val)) return mid;
else high = mid - 1;
}
}
return -1;
}
/**
* 查找最后一个值等于给定值的索引
*/
public static int searchLast(int[] arr, int val) {
int low = 0, high = arr.length - 1, mid;
while (low <= high) {
// 如果数组很大，low + high可能会发生溢出
mid = low + (high - low)/2;
if (arr[mid] < val) {
low = mid + 1;
} else if (arr[mid] > val) {
high = mid - 1;
} else {
// 判断是否最后一个位置
if (mid == arr.length - 1 || (arr[mid + 1] != val)) return mid;
else low = mid + 1;
}
}
return -1;
}
/**
* 查找第一个大于等于给定值的索引
*/
public static int searchFirstBigger(int[] arr, int val) {
int low = 0, high = arr.length - 1, mid;
while (low <= high) {
// 如果数组很大，low + high可能会发生溢出
mid = low + (high - low)/2;
if (arr[mid] >= val) {
if (mid == 0 || (arr[mid - 1] != val)) return mid;
high = mid - 1;
} else {
low = mid + 1;
}
}
return -1;
}
/**
* 查找最后一个小于等于给定值的元素
*/
public static int searchLastSmaller(int[] arr, int val) {
int low = 0, high = arr.length - 1, mid;
while (low <= high) {
// 如果数组很大，low + high可能会发生溢出
mid = low + (high - low)/2;
if (arr[mid] > val) {
high = mid - 1;
} else {
if (mid == arr.length - 1 || (arr[mid + 1] > val)) return mid;
low = mid + 1;
}
}
return -1;
}
/**
* 求解平方根
*/
public static double sqrt(double val, int precision) {
if (val <= 0 || precision < 0) return 0.0;
double p = 1.0 / Math.pow(10, precision);
double low = 0;
double high = val;
double guess = low + (high - low)/2;
double diff = guess * guess - val;
while (Math.abs(diff) > p) {
if (diff > 0) {
high = guess;
} else {
low = guess;
}
guess = low + (high - low)/2;
diff = guess * guess - val;
}
return guess;
}
}