二维数组中的查找
在一个二维数组中(每个一维数组的长度相同),每一行都按照从左到右递增的顺序排序,每一列都按照从上到下递增的顺序排序。请完成一个函数,输入这样的一个二维数组和一个整数,判断数组中是否含有该整数。
思路:先在对角线处二分,
当这个点的值等于目标点的值时,返回true
当这个点的值小于目标点的值时,分别二分查找该点右侧和下侧的所有数。
当这个点的值大于目标点的值时,分别二分查找该点左侧和上侧的所有数
public class Solution { public boolean Find(int target, int [][] array) { int upRow = 0; int downRow = array.length-1; int leftCol = 0; int rightCol = array[0].length-1; while(true) { if(upRow > downRow) break; if(leftCol > rightCol) break; int midRow = (upRow+downRow)/2; int midCol = (leftCol+rightCol)/2; if(array[midRow][midCol] == target) return true; else if(array[midRow][midCol] < target) { if(array[midRow][array[0].length-1]==target || array[array.length-1][midCol]==target ) return true; if(array[midRow][array[0].length-1] > target) { int left = midCol+1; int right = array[0].length-1; int midc; while(left<=right) { midc = (left+right)/2; if(array[midRow][midc] == target) return true; else if(array[midRow][midc] < target) left = midc + 1; else right = midc - 1; } } if(array[array.length-1][midCol] > target) { int left = midRow+1; int right = array.length-1; while(left<=right) { int midr = (left+right)/2; if(array[midr][midCol] == target) return true; else if(array[midr][midCol] < target) left = midr + 1; else right = midr - 1; } } leftCol = midCol + 1; upRow = midRow + 1; } else if(array[midRow][midCol] > target) { if(array[midRow][0]==target || array[0][midCol]==target ) return true; if(array[midRow][0] < target) { int left = 0; int right = midCol-1; int midc; while(left<=right) { midc = (left+right)/2; if(array[midRow][midc] == target) return true; else if(array[midRow][midc] < target) left = midc + 1; else right = midc - 1; } } if(array[0][midCol] < target) { int left = 0; int right = midRow-1; while(left<=right) { int midr = (left+right)/2; if(array[midr][midCol] == target) return true; else if(array[midr][midCol] < target) left = midr + 1; else right = midr - 1; } } rightCol = midCol - 1; downRow = midRow - 1; } } return false; } }
优秀题解:左上角为最小点,右下角为最大点,选取左下角或右上角的点(可以视为中间点),从中间点开始,不断目标点比较,目标点大则往右或下移动,反之则往上或左移动。
public class Solution { public boolean Find(int [][] array,int target) { int len = array.length-1; int i = 0; while((len >= 0)&& (i < array[0].length)){ if(array[len][i] > target){ len--; }else if(array[len][i] < target){ i++; }else{ return true; } } return false; } }