在有序数组中确定num是否存在

Java实现

public static boolean exist(int[] arr, int num) {if (arr == null || arr.length == 0) {return false;}int L = 0；int R = arr.length - 1;int M = 0;while (L <= R) {M = (L + R) / 2;if (arr[M] == num) {return true;} else if (arr[M] > num) {R = M - 1;} else {L = M + 1;}}return false;}

C语言实现

int exist(int arr[], int length, int num) {if (arr == NULL || length == 0) {return 0;}int L = 0;int R = length - 1;int M = 0;while (L <= R) {M = (L + R) / 2;if (arr[M] == num) {return 1;}else if (arr[M] < num) {L = M + 1;}else {R = M - 1;}}return 0;
}

在有序数组中找>=num的最左位置

Java实现

public static int findLeftIndex(int[] arr, int num) {int L = 0;int R = arr.length - 1;int M = 0;int Index = -1;while (L <= R) {M = (L + R) / 2;  // 数组长度很长的时候有溢出风险// M = L + (R - L) / 2;// M = L + ((R - L) >> 1);if (arr[M] >= num) {Index = M;R = M - 1;} else {L = M + 1;}}return Index;}

C语言实现

int findLeftIndex(int arr[], int length, int num) {int R = length - 1;int L = 0;int M = 0;int Index = -1;while (L <= R) {M = (R + L) / 2;if (arr[M] >= num) {Index = M;R = M - 1;}else {L = M + 1;}}return Index;	
}

在有序数组中找<=num的最右位置

Java实现

public static int findRightIndex(int[] arr, int num) {int L = 0;int R = arr.length - 1;int M = 0;int Index = -1;while (L <= R) {M = (L + R) / 2; if (arr[M] <= num) {Index = M;L = M + 1;} else {R = M - 1;}}return Index;}

C语言实现

int findRightIndex(int arr[], int length, int num) {int R = length - 1;int L = 0;int M = 0;int Index = -1;while (L <= R) {M = (R + L) / 2;if (arr[M] <= num) {Index = M;L = M + 1;} else {R = M - 1;}}return Index;
}