算法基础之二分查找之二

import java.util.Arrays;

/**
 * 二分查找,在有序数组中找到大于等于num最左的位置
 */
public class Code02_BSNearLeft {
    public static void main(String[] args) {
        int maxLen = 50;
        int maxValue = 100;
        int testTime = 100000;
        for (int i = 0; i < testTime; i++) {
            int[] arr = lenRandomValueRandom(maxLen, maxValue);
            int value = (int) ((maxValue + 1) * Math.random()) - (int) (maxValue * Math.random());
            Arrays.sort(arr);
            if(test(arr,value) != find(arr,value)) {
                System.out.println("出错了！");
                printArray(arr);
            }
        }
    }

    public static void printArray(int[] arr) {
        for (int i = 0; i < arr.length; i++) {
            System.out.print(arr[i] + " ");
        }
    }

    public static int test(int[] arr, int findValue) {
        for (int i = 0; i < arr.length; i++) {
            if(arr[i] >= findValue) {
                return i;
            }
        }
        return -1;
    }
    public static int find(int[] arr, int findValue) {
        if(arr == null || arr.length == 0) {
            return -1;
        }
        int L = 0;
        int R = arr.length - 1;
        int t = -1;
        while (L <= R){
            int mid = (L+R)/2;
            if(arr[mid] >= findValue) {
                t = mid;
                R = mid - 1;
            } else {
                L = mid + 1;
            }
        }
        return t;
    }

    // 返回一个数组arr，arr长度[0,maxLen-1],arr中的每个值[0,maxValue-1]
    public static int[] lenRandomValueRandom(int maxLen, int maxValue) {
        int len = (int) (Math.random() * maxLen);
        int[] arr = new int[len];
        for (int i = 0; i < len; i++) {
            int value = (int) (Math.random() * maxValue);
            arr[i] = value;
        }
        return arr;
    }

}