二分查找
public static int find(int[] arr, int target) { int l = 0; int r = arr.length - 1; int mid = 0; while (l <= r) { mid = (l+r)/2; if (arr[mid] == target) { return mid; } else if (arr[mid] > target) { r = mid - 1; } else { l = mid + 1; } } return -1; }