Java实现二分法变种的示例代码

public int findFirstEqual(int[] nums, int target) {
    int left = 0, right = nums.length - 1;
    while (left <= right) {
        int mid = left + (right - left) / 2;
        if (nums[mid] >= target) {
            right = mid - 1; // 继续向左查找
        } else {
            left = mid + 1;
        }
    }
    // 检查left是否越界以及nums[left]是否等于target
    if (left >= 0 && nums[left] == target) {
        return left;
    } else {
        return -1; // 未找到
    }
}

public int findLastEqual(int[] nums, int target) {
    int left = 0, right = nums.length - 1;
    while (left <= right) {
        int mid = left + (right - left) / 2;
        if (nums[mid] > target) {
            right = mid - 1;
        } else {
            left = mid + 1; // 继续向右查找
        }
    }
    // 检查right是否越界以及nums[right]是否等于target
    if (right >= 0 && nums[right] == target) {
        return right;
    } else {
        return -1; // 未找到
    }
}

public int searchInsert(int[] nums, int target) {
    int left = 0, right = nums.length - 1;
    while (left <= right) {
        int mid = left + (right - left) / 2;
        if (nums[mid] == target) {
            return mid; // 找到目标元素，返回其索引
        } else if (nums[mid] < target) {
            left = mid + 1; // 目标元素在右半部分
        } else {
            right = mid - 1; // 目标元素在左半部分或不存在（此时right指向的位置应插入target）
        }
    }
    // 未找到目标元素，返回应插入的位置
    return left;
}