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58 lines
1.8 KiB
58 lines
1.8 KiB
/**
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* File: binary_search_edge.cpp
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* Created Time: 2023-05-21
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* Author: Krahets (krahets@163.com)
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*/
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#include "../utils/common.hpp"
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/* 二分查找最左一个元素 */
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int binarySearchLeftEdge(vector<int> &nums, int target) {
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int i = 0, j = nums.size() - 1; // 初始化双闭区间 [0, n-1]
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while (i <= j) {
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int m = i + (j - i) / 2; // 计算中点索引 m
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if (nums[m] < target)
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i = m + 1; // target 在区间 [m+1, j] 中
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else if (nums[m] > target)
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j = m - 1; // target 在区间 [i, m-1] 中
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else
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j = m - 1; // 首个小于 target 的元素在区间 [i, m-1] 中
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}
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if (i == nums.size() || nums[i] != target)
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return -1; // 未找到目标元素，返回 -1
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return i;
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}
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/* 二分查找最右一个元素 */
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int binarySearchRightEdge(vector<int> &nums, int target) {
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int i = 0, j = nums.size() - 1; // 初始化双闭区间 [0, n-1]
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while (i <= j) {
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int m = i + (j - i) / 2; // 计算中点索引 m
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if (nums[m] < target)
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i = m + 1; // target 在区间 [m+1, j] 中
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else if (nums[m] > target)
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j = m - 1; // target 在区间 [i, m-1] 中
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else
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i = m + 1; // 首个大于 target 的元素在区间 [m+1, j] 中
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}
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if (j < 0 || nums[j] != target)
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return -1; // 未找到目标元素，返回 -1
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return j;
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}
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/* Driver Code */
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int main() {
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int target = 6;
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vector<int> nums = {1, 3, 6, 6, 6, 6, 6, 10, 12, 15};
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// 二分查找最左一个元素
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int indexLeft = binarySearchLeftEdge(nums, target);
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cout << "数组中最左一个元素 6 的索引 = " << indexLeft << endl;
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// 二分查找最右一个元素
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int indexRight = binarySearchRightEdge(nums, target);
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cout << "数组中最右一个元素 6 的索引 = " << indexRight << endl;
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return 0;
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}
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