迫于考试，请教各位大佬一个 Java 二分查找算法

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题目：给定一个递增排序的数组，查找某个数字是否在数组中，如果在数组中，则返回该数字在数组中第一次出现的位置（从 0 开始）；如果不在数组中，返回-1 。务必使用二分查找的方式

哪位好心人可以贴下代码

Supplement 1 · Apr 16, 2021

此贴结

查找

给定

Java

4 replies

zm8m93Q1e5otOC69

Apr 15, 2021

这不就是二分查找吗？百度一下都有

zm8m93Q1e5otOC69

Apr 15, 2021

public static int binarySearch(int[] arrays, int key, int start, int end) {
if (key < arrays[start] || key > arrays[end] || start > end) {
return -1;
}
int mid = (start + end) / 2;
if (arrays[mid] > key) {
return binarySearch(arrays, key, start, mid - 1);
} else if (arrays[mid] < key) {
return binarySearch(arrays, key, mid + 1, end);
} else {
return mid;
}
}

zm8m93Q1e5otOC69

Apr 15, 2021

jdk 的写法
// Like public version, but without range checks.
private static int binarySearch0(int[] a, int fromIndex, int toIndex,
int key) {
int low = fromIndex;
int high = toIndex - 1;

while (low <= high) {
int mid = (low + high) >>> 1;
int midVal = a[mid];

if (midVal < key)
low = mid + 1;
else if (midVal > key)
high = mid - 1;
else
return mid; // key found
}
return -(low + 1); // key not found.
}

KissFace

Apr 16, 2021

@beichenhpy 谢谢老哥