给定一个包含 0 和 1 的二进制矩阵mat[][] 。矩阵的每一行都按非递减顺序排序，任务是找到矩阵最左边的列中至少有一个 1。
注意：如果不存在这样的列，则返回 -1。
例子：
Input:
mat[2][2] = { {0, 0},
{1, 1} }
Output: 1
Explanation:
The 1st column of the
matrix contains atleast a 1.
Input:
mat[2][2] = {{0, 0},
{0, 0}}
Output: -1
Explanation:
There is no such column which
contains atleast one 1.方法：这个想法是迭代矩阵的所有行并在它们上进行二分搜索，以在该行中第一次出现 1。矩阵行中第一个 1 的所有出现中的最小值将是问题的所需解决方案。
下面是上述方法的实现：
C++
// C++ implementation to find the
// Leftmost Column with atleast a
// 1 in a sorted binary matrix
#include
#define N 3
using namespace std;
// Function to search for the
// leftmost column of the matrix
// with atleast a 1 in sorted
// binary matrix
int search(int mat[][3], int n, int m)
{
int i, a = INT_MAX;
// Loop to iterate over all the
// rows of the matrix
for (i = 0; i < n; i++) {
int low = 0;
int high = m - 1;
int mid;
int ans = INT_MAX;
// Binary Search to find the
// leftmost occurence of the 1
while (low <= high) {
mid = (low + high) / 2;
// Condition if the column
// contains the 1 at this
// position of matrix
if (mat[i][mid] == 1) {
if (mid == 0) {
ans = 0;
break;
}
else if (mat[i][mid - 1] == 0) {
ans = mid;
break;
}
}
if (mat[i][mid] == 1)
high = mid - 1;
else
low = mid + 1;
}
// If there is a better solution
// then update the answer
if (ans < a)
a = ans;
}
// Condition if the solution
// doesn't exist in the matrix
if (a == INT_MAX)
return -1;
return a+1;
}
// Driver Code
int main()
{
int mat[3][3] = { 0, 0, 0,
0, 0, 1,
0, 1, 1 };
cout << search(mat, 3, 3);
return 0;
} Java
// Java implementation to find the
// Leftmost Column with atleast a
// 1 in a sorted binary matrix
import java.util.*;
class GFG{
static final int N = 3;
// Function to search for the
// leftmost column of the matrix
// with atleast a 1 in sorted
// binary matrix
static int search(int mat[][], int n, int m)
{
int i, a = Integer.MAX_VALUE;
// Loop to iterate over all the
// rows of the matrix
for(i = 0; i < n; i++)
{
int low = 0;
int high = m - 1;
int mid;
int ans = Integer.MAX_VALUE;
// Binary Search to find the
// leftmost occurence of the 1
while (low <= high)
{
mid = (low + high) / 2;
// Condition if the column
// contains the 1 at this
// position of matrix
if (mat[i][mid] == 1)
{
if (mid == 0)
{
ans = 0;
break;
}
else if (mat[i][mid - 1] == 0)
{
ans = mid;
break;
}
}
if (mat[i][mid] == 1)
high = mid - 1;
else
low = mid + 1;
}
// If there is a better solution
// then update the answer
if (ans < a)
a = ans;
}
// Condition if the solution
// doesn't exist in the matrix
if (a == Integer.MAX_VALUE)
return -1;
return a + 1;
}
// Driver Code
public static void main(String[] args)
{
int mat[][] = { { 0, 0, 0 },
{ 0, 0, 1 },
{ 0, 1, 1 } };
System.out.print(search(mat, 3, 3));
}
}
// This code is contributed by Amit KatiyarPython3
# Python3 implementation to find the
# Leftmost Column with atleast a
# 1 in a sorted binary matrix
import sys
N = 3
# Function to search for the
# leftmost column of the matrix
# with atleast a 1 in sorted
# binary matrix
def search(mat, n, m):
a = sys.maxsize
# Loop to iterate over all the
# rows of the matrix
for i in range (n):
low = 0
high = m - 1
ans = sys.maxsize
# Binary Search to find the
# leftmost occurence of the 1
while (low <= high):
mid = (low + high) // 2
# Condition if the column
# contains the 1 at this
# position of matrix
if (mat[i][mid] == 1):
if (mid == 0):
ans = 0
break
elif (mat[i][mid - 1] == 0):
ans = mid
break
if (mat[i][mid] == 1):
high = mid - 1
else:
low = mid + 1
# If there is a better solution
# then update the answer
if (ans < a):
a = ans
# Condition if the solution
# doesn't exist in the matrix
if (a == sys.maxsize):
return -1
return a + 1
# Driver Code
if __name__ == "__main__":
mat = [[0, 0, 0],
[0, 0, 1],
[0, 1, 1]]
print(search(mat, 3, 3))
# This code is contributed by ChitranayalC#
// C# implementation to find the leftmost
// column with atleast a 1 in a sorted
// binary matrix
using System;
class GFG{
//static readonly int N = 3;
// Function to search for the leftmost
// column of the matrix with atleast a
// 1 in sorted binary matrix
static int search(int [,]mat, int n, int m)
{
int i, a = int.MaxValue;
// Loop to iterate over all the
// rows of the matrix
for(i = 0; i < n; i++)
{
int low = 0;
int high = m - 1;
int mid;
int ans = int.MaxValue;
// Binary Search to find the
// leftmost occurence of the 1
while (low <= high)
{
mid = (low + high) / 2;
// Condition if the column
// contains the 1 at this
// position of matrix
if (mat[i, mid] == 1)
{
if (mid == 0)
{
ans = 0;
break;
}
else if (mat[i, mid - 1] == 0)
{
ans = mid;
break;
}
}
if (mat[i, mid] == 1)
high = mid - 1;
else
low = mid + 1;
}
// If there is a better solution
// then update the answer
if (ans < a)
a = ans;
}
// Condition if the solution
// doesn't exist in the matrix
if (a == int.MaxValue)
return -1;
return a + 1;
}
// Driver Code
public static void Main(String[] args)
{
int [,]mat = { { 0, 0, 0 },
{ 0, 0, 1 },
{ 0, 1, 1 } };
Console.Write(search(mat, 3, 3));
}
}
// This code is contributed by Amit KatiyarJavascript
输出：
2性能分析：
- 时间复杂度： O(N*logN)
- 辅助空间： O(1)
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