🔗 https://leetcode.cn/problems/search-a-2d-matrix

题目

• 给一个二维矩阵，保证数字在每行从左到右都是非严格递增
• 每一行的第一个数字大于上一行最后一个数字
• 给一个 target，判断是否存在在二维矩阵中

思路

• 先 binary search 定位到行，再 binary search 定位到列

代码

class Solution {
public:bool searchMatrix(vector<vector<int>>& matrix, int target) {int m = matrix.size();int n = matrix[0].size();int x, y, xx, yy;x = 0; y = 0; xx = m - 1; yy = n - 1;int mid_x = (x + xx) / 2;while (x <= xx) {mid_x = (x + xx) / 2;if (matrix[mid_x][n - 1] < target) {x = mid_x + 1;}if (matrix[mid_x][0] > target) {xx = mid_x - 1;}if (matrix[mid_x][0] <= target && matrix[mid_x][n - 1] >= target)break;}if (matrix[mid_x][0] > target || matrix[mid_x][n - 1] < target) return false;int mid_y = (y + yy) / 2;while (y <= yy) {int mid_y = (y + yy) / 2;if (matrix[mid_x][mid_y] == target) return true;if (matrix[mid_x][mid_y] < target) {y = mid_y + 1;} else {yy = mid_y - 1;}  }return false;}
};