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Code04_BSAwesome.java
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90 lines (82 loc) · 1.94 KB
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package class03;
public class Code04_BSAwesome {
// arr 相邻的数不相等！
public static int oneMinIndex(int[] arr) {
if (arr == null || arr.length == 0) {
return -1;
}
int N = arr.length;
if (N == 1) {
return 0;
}
if (arr[0] < arr[1]) {
return 0;
}
if (arr[N - 1] < arr[N - 2]) {
return N - 1;
}
int L = 0;
int R = N - 1;
// L...R 肯定有局部最小
while (L < R - 1) {
int mid = (L + R) / 2;
if (arr[mid] < arr[mid - 1] && arr[mid] < arr[mid + 1]) {
return mid;
} else {
if (arr[mid] > arr[mid - 1]) {
R = mid - 1;
} else {
L = mid + 1;
}
}
}
return arr[L] < arr[R] ? L : R;
}
// 生成随机数组，且相邻数不相等
public static int[] randomArray(int maxLen, int maxValue) {
int len = (int) (Math.random() * maxLen);
int[] arr = new int[len];
if (len > 0) {
arr[0] = (int) (Math.random() * maxValue);
for (int i = 1; i < len; i++) {
do {
arr[i] = (int) (Math.random() * maxValue);
} while (arr[i] == arr[i - 1]);
}
}
return arr;
}
// 也用于测试
public static boolean check(int[] arr, int minIndex) {
if (arr.length == 0) {
return minIndex == -1;
}
int left = minIndex - 1;
int right = minIndex + 1;
boolean leftBigger = left >= 0 ? arr[left] > arr[minIndex] : true;
boolean rightBigger = right < arr.length ? arr[right] > arr[minIndex] : true;
return leftBigger && rightBigger;
}
public static void printArray(int[] arr) {
for (int num : arr) {
System.out.print(num + " ");
}
System.out.println();
}
public static void main(String[] args) {
int maxLen = 100;
int maxValue = 200;
int testTime = 1000000;
System.out.println("测试开始");
for (int i = 0; i < testTime; i++) {
int[] arr = randomArray(maxLen, maxValue);
int ans = oneMinIndex(arr);
if (!check(arr, ans)) {
printArray(arr);
System.out.println(ans);
break;
}
}
System.out.println("测试结束");
}
}