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Solution34.cpp
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100 lines (98 loc) · 2.53 KB
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//
// Solution34.cpp
// Algorithm
//
// Created by Pancf on 2020/10/17.
// Copyright © 2020 Pancf. All rights reserved.
//
#include "Solution34.hpp"
std::vector<int> Solution34::searchRange(std::vector<int> &nums, int target)
{
// metho1, method1耗时比method2耗时更短的原因是method1更早剪枝
if (nums.size() == 0) return {-1, -1};
std::vector<int> res;
int lo = 0, hi = (int)nums.size() - 1;
int pivot = -1;
while (lo <= hi) {
int mid = (lo + hi) / 2;
if (nums[mid] == target) {
pivot = mid;
break;
} else if (nums[mid] > target && nums[lo] <= target) {
// [lo, mid)
hi = mid - 1;
} else if (nums[mid] < target && target <= nums[hi]) {
// (mid, hi]
lo = mid + 1;
} else {
break;
}
}
if (pivot == -1) return {-1, -1};
// come here, means nums[pivot] == target
lo = 0;
hi = pivot;
// find lower bound
while (lo < hi) {
int mid = (lo + hi) / 2;
if (nums[mid] < target) {
// [lo, mid]被剪枝
lo = mid + 1;
} else {
// nums[mid] == target
hi = mid;
}
}
res.push_back(lo);
lo = pivot;
hi = (int)nums.size() - 1;
// find upper bound
while (lo < hi) {
// +1 非常重要，mid需要取ceil
int mid = (lo + hi + 1) / 2;
if (nums[mid] > target) {
// [mid, hi]被剪枝
hi = mid - 1;
} else {
// nums[mid] == target
lo = mid;
}
}
res.push_back(hi);
return res;
// method2
// std::vector<int> res{-1, -1};
// if (nums.size() == 0) return res;
// int lo = 0, hi = (int)nums.size() - 1;
// // find lower bound
// while (lo < hi) {
// int mid = (lo + hi) / 2;
// if (nums[mid] < target) {
// // cut [lo, mid]
// lo = mid + 1;
// } else {
// hi = mid;
// }
// }
// if (target == nums[lo]) {
// res[0] = lo;
// } else {
// // early prune
// return res;
// }
// // it is unnacessary to reset lo
// hi = (int)nums.size() - 1;
// // find upper bound
// while (lo < hi) {
// // +1 is important which makes mid ceiling
// int mid = (lo + hi + 1) / 2;
// if (nums[mid] > target) {
// // cut [mid, hi]
// hi = mid - 1;
// } else {
// lo = mid;
// }
// }
// res[1] = target == nums[lo] ? lo : -1;
// return res;
}